Pharmaceutical Formulations: Dispersed Systems Quiz
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Questions and Answers

What are multi-phase (dispersed) systems in pharmaceutical formulations?

  • Gels (correct)
  • Emulsions (correct)
  • Suspensions (correct)
  • Solutions

    • Dispersed systems have a homogenous appearance.

    False

    What is an example of a non-Newtonian fluid?

    Ketchup

    Emulsifying agents facilitate the dispersion of two ______ liquids.

    <p>immiscible</p> Signup and view all the answers

    Dispersed systems have a rapid onset of action compared to solid dosage forms.

    <p>True</p> Signup and view all the answers

    A surfactant reduces ______ tension.

    <p>interfacial</p> Signup and view all the answers

    What is the purpose of a suspending agent?

    <p>To reduce sedimentation rate of particles.</p> Signup and view all the answers

    Which of the following is a disadvantage of dispersed systems?

    <p>Non-homogeneous</p> Signup and view all the answers

    The ability of a liquid to displace air and spread over solid particles is known as ______.

    <p>wetting</p> Signup and view all the answers

    What does a higher Zeta (ζ) potential indicate?

    <p>More stable suspension</p> Signup and view all the answers

    Emulsions are thermodynamically stable.

    <p>False</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Wetting = Ability of a liquid to displace air and spread over solid particles Zeta Potential = Controls the degree of repulsion between similarly charged particles Emulsifying Agent = Substance that stabilizes an emulsion Non-Newtonian Fluid = Viscosity changes when force is applied</p> Signup and view all the answers

    What is the required HLB for the formulation discussed?

    <p>14.3</p> Signup and view all the answers

    The HLB of Tween 80 is ______.

    <p>15</p> Signup and view all the answers

    The HLB of Span 80 is ______.

    <p>4.3</p> Signup and view all the answers

    What happens to emulsions when temperature extremes are encountered?

    <p>Phase inversion can occur.</p> Signup and view all the answers

    Which method uses acacia as an emulsifier?

    <p>Both methods</p> Signup and view all the answers

    O/W emulsions can be diluted with water.

    <p>True</p> Signup and view all the answers

    What defines a microemulsion?

    <p>Consists of large micelles containing the internal phase.</p> Signup and view all the answers

    Match each emulsifier with its HLB value:

    <p>Tween 80 = 15 Span 80 = 4.3 Tween 40 = 15.6 Span 60 = 4.7</p> Signup and view all the answers

    In the emulsification, the ratio of fixed oil, water, and acacia should be ______.

    <p>4 parts fixed oil : 2 parts water : 1 part emulsifier</p> Signup and view all the answers

    What are the three types of emulsifiers?

    <p>Hydrophilic colloids</p> Signup and view all the answers

    What is a common commercial product mentioned for oral use?

    <p>Microlipid®</p> Signup and view all the answers

    What is the expected quality of an emulsifier regarding its compatibility?

    <p>Should not affect the stability and efficacy of the product</p> Signup and view all the answers

    Flocculated suspensions sediment slowly.

    <p>False</p> Signup and view all the answers

    Natural hydrophilic colloids are less commonly used in the food industry than in pharmaceuticals.

    <p>False</p> Signup and view all the answers

    What is the role of the emulsifying agent in an emulsion?

    <p>To stabilize the mixture</p> Signup and view all the answers

    Which of the following is an example of a hydrophilic colloid?

    <p>Casein</p> Signup and view all the answers

    How do surfactants function in emulsification?

    <p>They reduce interfacial tension between oil and water.</p> Signup and view all the answers

    Intravenous fat emulsions are used in ______ nutrition support.

    <p>total parenteral</p> Signup and view all the answers

    Which class of surfactants has a hydrophilic portion that contains a negative charge?

    <p>Anionic surfactants</p> Signup and view all the answers

    What is the HLB system used for?

    <p>It measures the balance between hydrophilicity and lipophilicity of surfactants.</p> Signup and view all the answers

    Surfactants with an HLB of _____ produce O/W emulsions.

    <p>8-18</p> Signup and view all the answers

    What is the role of bile salts in the digestive process?

    <p>They enhance fat digestion and absorption.</p> Signup and view all the answers

    What type of surfactant is sodium lauryl sulfate?

    <p>Anionic surfactant</p> Signup and view all the answers

    Hydrophobic portion of surfactants remains oriented in the __________ phase.

    <p>non-aqueous</p> Signup and view all the answers

    What is the formula for the degree of flocculation?

    <p>β = F / F∞</p> Signup and view all the answers

    What does Stokes’ law express?

    <p>All of the above</p> Signup and view all the answers

    Larger particles fall more slowly than smaller particles according to Stokes’ law.

    <p>False</p> Signup and view all the answers

    Which factor is inversely proportional to the rate of sedimentation?

    <p>Viscosity of the dispersion medium</p> Signup and view all the answers

    What are the typical components of oral suspension dosage forms?

    <p>Active ingredient, wetting agent, dispersion medium, suspending agent, sweetener/flavor, flocculating agent, preservative.</p> Signup and view all the answers

    Which of the following factors contributes to the difficulty of redistributing a suspension after sedimentation?

    <p>B &amp; C</p> Signup and view all the answers

    What typically occurs due to the conversion from meta-stable to stable forms in suspensions?

    <p>Change in physical stability, solubility, dissolution rate, and bioavailability.</p> Signup and view all the answers

    Gels consist exclusively of small inorganic particles and contain no organic molecules.

    <p>False</p> Signup and view all the answers

    What type of gel is characterized by the presence of a three-dimensional network restricting the movement of the dispersing medium?

    <p>Single-phase gels</p> Signup and view all the answers

    The expulsion of a liquid from a gel is known as ________.

    <p>syneresis</p> Signup and view all the answers

    What is a common use for bentonite magma?

    <p>As a thickener in calamine lotion.</p> Signup and view all the answers

    What is the degree of flocculation defined as?

    <p>β = F / F∞</p> Signup and view all the answers

    Which law expresses the velocity of sedimentation?

    <p>Stokes' Law</p> Signup and view all the answers

    What factors are inversely proportional to the rate of sedimentation?

    <p>Viscosity of the dispersion medium</p> Signup and view all the answers

    Which of the following typically increases the difficulty of redistributing a suspension after sedimentation?

    <p>b &amp; c</p> Signup and view all the answers

    The ______ is the acceleration due to gravity.

    <p>980.7 cm/sec²</p> Signup and view all the answers

    Match the following components of oral suspension dosage forms:

    <p>Active ingredient = The therapeutic substance Wetting agent = Facilitates dispersion Suspending agent = Keeps particles afloat Preservative = Prevents microbial growth</p> Signup and view all the answers

    What is required for packaging and storing suspensions?

    <p>Light resistant, airtight containers</p> Signup and view all the answers

    Which of the following is NOT a type of emulsifier?

    <p>Emulsifying solids</p> Signup and view all the answers

    What are the three types of emulsifiers?

    <p>Hydrophilic colloids, finely divided solid particles, surfactants</p> Signup and view all the answers

    Hydrophilic colloids can cause an appreciable lowering in surface tension.

    <p>False</p> Signup and view all the answers

    Name two examples of natural hydrophilic colloids.

    <p>Acacia and gelatin</p> Signup and view all the answers

    Surfactants can only be used in oil-in-water (O/W) emulsions.

    <p>False</p> Signup and view all the answers

    What is the role of bile salts in the digestive process?

    <p>Emulsify fats</p> Signup and view all the answers

    What does the HLB system measure?

    <p>The balance between hydrophilicity and lipophilicity of surfactants</p> Signup and view all the answers

    Surfactants with an HLB of 4-6 produce __________ emulsions.

    <p>W/O</p> Signup and view all the answers

    Give an example of a surfactant with a high HLB value.

    <p>Tween 80</p> Signup and view all the answers

    What happens to a surfactant at its CMC (Critical Micelle Concentration)?

    <p>It starts forming micelles</p> Signup and view all the answers

    Which of the following are examples of multi-phase (dispersed) systems?

    <p>All of the above</p> Signup and view all the answers

    Dispersed systems are always homogenous.

    <p>False</p> Signup and view all the answers

    What does a 'Shake Well' label indicate?

    <p>The preparation must be mixed to redistribute the dispersed particles.</p> Signup and view all the answers

    A dispersed phase is also known as the ______.

    <p>internal phase</p> Signup and view all the answers

    What is the main advantage of using dispersed systems?

    <p>Easy to swallow</p> Signup and view all the answers

    Dispensed systems tend to be bulky compared to solid dosage forms.

    <p>True</p> Signup and view all the answers

    What is the role of emulsifying agents in multi-phase liquids?

    <p>To facilitate the dispersion of two immiscible liquids and stabilize them.</p> Signup and view all the answers

    The term ‘wetting’ refers to a liquid's ability to ______.

    <p>displace air and spread over the surface of solid particles</p> Signup and view all the answers

    What happens when Zeta (ζ) potential is below a threshold value?

    <p>Particles aggregate</p> Signup and view all the answers

    Describe interfacial tension.

    <p>The force of attraction between the molecules at the interface of two fluids.</p> Signup and view all the answers

    Oil-in-water emulsions consist of oil dispersed in ______.

    <p>water</p> Signup and view all the answers

    What does Bancroft’s Rule state?

    <p>The phase in which an emulsifier is more soluble is the continuous phase.</p> Signup and view all the answers

    A good emulsion should have particles that aggregate quickly.

    <p>False</p> Signup and view all the answers

    What is rheology?

    <p>The branch of physics that deals with the deformation and flow of matter.</p> Signup and view all the answers

    What is the required HLB in the calculation lectures?

    <p>14.3</p> Signup and view all the answers

    How much total emulsifier is used in a 100 g total formulation with 2% w/v?

    <p>2 g</p> Signup and view all the answers

    Which of the following is the HLB of Tween 80?

    <p>15</p> Signup and view all the answers

    Which of the following methods is used for emulsification?

    <p>Both A and B</p> Signup and view all the answers

    Match the following emulsifiers with their respective HLB values:

    <p>Tween 80 = 15 Span 80 = 4.3 Tween 40 = 15.6 Span 60 = 4.7</p> Signup and view all the answers

    What is the phase volume ratio at which an emulsion is most stable?

    <p>50:50</p> Signup and view all the answers

    What should not be done to prevent emulsion phase inversion?

    <p>Do not freeze or leave in a hot car</p> Signup and view all the answers

    O/W emulsions can be easily diluted with water.

    <p>True</p> Signup and view all the answers

    W/O emulsions will conduct electricity.

    <p>False</p> Signup and view all the answers

    What are two major types of emulsions?

    <p>O/W and W/O</p> Signup and view all the answers

    What type of emulsifier is acacia?

    <p>Natural emulsifier</p> Signup and view all the answers

    What is the purpose of integrating drugs during emulsion formation?

    <p>For chemical stability and efficacy</p> Signup and view all the answers

    Define the various categories of excipients used in multi-phase liquid dosage forms.

    <p>Excipients can be categorized based on their function such as fillers, binders, disintegrants, lubricants, preservatives, and more.</p> Signup and view all the answers

    Why is wetting of solids a potential problem?

    <p>Wetting of solids can hinder the formation of drug solutions and affect drug bioavailability.</p> Signup and view all the answers

    How can wetting be improved?

    <p>Wetting can be improved by using surfactants, increasing the temperature, or changing the vehicle's composition.</p> Signup and view all the answers

    What is the contact angle of a completely wetted solid?

    <p>The contact angle of a completely wetted solid is 0 degrees.</p> Signup and view all the answers

    How can particle aggregation be avoided?

    <p>Particle aggregation can be avoided by using additives like surfactants or maintaining appropriate pH and ionic strength.</p> Signup and view all the answers

    Define surface tension.

    <p>Surface tension is the energy required to increase the surface area of a liquid due to cohesive forces among its molecules.</p> Signup and view all the answers

    Define interfacial tension.

    <p>Interfacial tension is the tension at the interface between two immiscible liquids or between a liquid and a solid.</p> Signup and view all the answers

    List the three categories of emulsifying agents.

    <p>The three categories of emulsifying agents are hydrocolloids, finely-divided particles, and surfactants.</p> Signup and view all the answers

    Define the four main categories of surfactants.

    <p>The four main categories of surfactants are anionic, cationic, nonionic, and amphoteric.</p> Signup and view all the answers

    List two examples of naturally occurring surfactants and their function in the body.

    <p>Examples include bile acids and phospholipids. They help with emulsifying fats and facilitating digestion.</p> Signup and view all the answers

    Describe the common pharmaceutical uses of surfactants.

    <p>Surfactants are used in drug formulations to enhance solubility, stabilize emulsions, and improve bioavailability.</p> Signup and view all the answers

    What is the HLB value and how is it calculated for an emulsion?

    <p>HLB stands for Hydrophilic-Lipophilic Balance, and it is calculated based on the HLB values of all components present in an emulsion.</p> Signup and view all the answers

    Describe the wet gum and dry gum methods of emulsion preparation.

    <p>The wet gum method involves mixing gum with water before adding oil, while the dry gum method mixes oil and gum before adding water.</p> Signup and view all the answers

    What types of oils may be emulsified by the Forbes method?

    <p>The Forbes method can emulsify fixed oils such as vegetable oils, but not essential oils due to their volatility.</p> Signup and view all the answers

    What is the difference between calcium soap emulsions and soft soap emulsions?

    <p>Calcium soap emulsions use calcium as an emulsifying agent, while soft soap emulsions are based on sodium soap.</p> Signup and view all the answers

    What are the three types of emulsion instability?

    <p>The three types are creaming, coalescence, and phase separation.</p> Signup and view all the answers

    List the features of a good suspension.

    <p>A good suspension should have uniform particle distribution, appropriate viscosity, and stability over time.</p> Signup and view all the answers

    What equation governs sedimentation velocity?

    <p>The equation governing sedimentation velocity is Stokes' Law.</p> Signup and view all the answers

    Define flocculation.

    <p>Flocculation is the process where fine particulates form agglomerates or flocs.</p> Signup and view all the answers

    Explain how a structured vehicle slows down sedimentation of a suspension.

    <p>A structured vehicle increases viscosity, thereby providing resistance to the movement of suspended particles.</p> Signup and view all the answers

    How does controlled flocculation improve suspension properties?

    <p>Controlled flocculation enhances stability and prevents rapid sedimentation of particles.</p> Signup and view all the answers

    What is the difference between clear and turbid gels?

    <p>Clear gels are transparent and free of particles, whereas turbid gels contain dispersed particles that scatter light.</p> Signup and view all the answers

    Define syneresis.

    <p>Syneresis is the expulsion of liquid from a gel upon aging or external pressure.</p> Signup and view all the answers

    Define imbibition.

    <p>Imbibition is the process by which a gel absorbs liquid and swells.</p> Signup and view all the answers

    Define swelling as it relates to gels.

    <p>Swelling refers to the increase in volume of a gel due to the absorption of a solvent.</p> Signup and view all the answers

    Study Notes

    Multi-Phase Systems

    • Pharmaceutical systems with particulate matter dispersed throughout a continuous phase
    • Examples include: suspensions, emulsions, gels, magmas
    • Characterized by an interface between two phases

    Dispersed Systems

    • Consist of solid particulate matter or a dispersed phase distributed throughout a dispersion medium
    • Considered heterogeneous systems
    • Require shaking to ensure homogeneity
    • Appear opaque
    • Exhibit increased viscosity
    • Demonstrate non-Newtonian flow, meaning viscosity changes with applied force

    Advantages of Dispersed Systems

    • Easy to swallow
    • Flexible dosing
    • Easy to administer
    • Rapid onset of action compared to solid dosage forms
    • Flexibility in modifying the onset of action

    Disadvantages of Dispersed Systems

    • Non-homogeneous
    • Tendency to separate
    • Bulkier than solid dosage forms
    • Potential for taste issues
    • Drug instability in liquid form
    • Dose accuracy concerns
    • Susceptibility to spills
    • Dependence on accurate measuring devices

    Additional Excipients in Multi-Phase Liquids

    • Emulsifying agents

      • Facilitate and stabilize dispersion of two immiscible liquids
      • Examples include: Polysorbate (Tween) 80, Span 80, Acacia

    • Encapsulating or solubilizing agents

      • Promote and maintain dispersion of finely subdivided droplets
      • Examples include: Acacia, Cetomacrogol, Cetyl alcohol, Glyceryl monostearate, Sorbitan monooleate

    Surfactants

    • Adsorb to interfaces between phases to reduce interfacial tension
    • Can function as detergents or emulsifying agents
    • Examples: Benzalkonium chloride, Polysorbate 80, Sodium lauryl sulfate

    Levigating Agent

    • Liquid used to reduce particle size of a powder by grinding
    • Ensures complete wetting and even dispersion of a solid ingredient in liquid or semisolid products
    • Displaces air from the surface of dry powders
    • Examples: Mineral oil, Glycerin, Propylene glycol

    Suspending Agent

    • Viscosity-increasing agent that reduces sedimentation rate of particles in a vehicle where they're not soluble
    • Examples: Bentonite, Carbomers (Carbopol®), Cellulose derivatives (MC, HEC, HPMC, HPC), Tragacanth, Polyvinyl alcohol

    Physical Pharmacy & Problems with Multi-Phase Systems

    • Wetting of solid particles

      • Critical for suspensions
      • Some solids float on the surface of water (or other liquids) due to lack of wetting
      • Examples: Talc, Charcoal
      • Wetting refers to a liquid's ability to displace air and spread over the entire surface of solid particles.

    Wetting of Solid Particles

    • Contact angle

      • Describes the degree of wetting
      • Determined by the nature of the liquid and solid surface
      • Hydrophilic surfaces are readily wetted, while hydrophobic surfaces are not.

    • Contact angle values:

      • 0°: Complete wetting
      • 0° to 90°: Readily wetted solids
      • 90° to 180°: Poorly wetted solids
      • 180°: Non-wetted

    Wetting of Solid Particles

    • Problems caused by insufficient wetting:

      • Inability to mix powder with liquids to form suspensions
      • Dissolution problems for ingredients in tablets and capsules, leading to incomplete absorption

    Particle Aggregation / Caking

    • Particle aggregation:

      • Small particles attract each other, forming larger, heavier particles that sediment out of suspension
      • Resuspendable by shaking.

    • Caking:

      • Formation of a solid mass at the bottom of a bottle
      • Agglomerated particles are difficult to resuspend

    • Prevention:

      • Development of surface charge by:
        • Ionization of surface groups
        • Adsorption of electrolytes
        • Adsorption of charged surfactants

    Zeta (ζ) Potential

    • Controls repulsion between similarly charged, dispersed particles
    • Higher zeta potential indicates a more stable suspension
    • When zeta potential is below a threshold value, attractive forces dominate, leading to particle aggregation and instability

    Interfacial Phenomena

    • Surface: Boundary between two phases, where one phase is a gas

    • Interface: Boundary between two immiscible phases

    • Surface tension:

      • Describes the interface between liquids and gases
      • Unbalanced molecular cohesive forces at the surface create a net attractive force towards the bulk of the liquid
      • Surface tends to contract like a stretched elastic membrane

    Surface Tension

    • Surface tension values differ based on:

      • Liquid type
      • Temperature
      • Presence of solutes (e.g., surfactants)

    Interfacial Tension

    • Force of attraction between molecules at the interface of two fluids
    • Also known as surface tension when referring to the air/liquid interface
    • Higher interfacial tension results in separation of the two liquids
    • Interfacial tension decreases with increasing temperature
    • Surfactants reduce interfacial tension by adsorbing to the interface

    Interfacial Tension and Energy

    • Interfacial tension (γs) is directly proportional to the energy required to increase the interfacial area (A) between two immiscible liquids:

      • ΔE = γs ΔA

    • Surfactants decrease interfacial tension, requiring less energy to increase the interfacial area and leading to smaller droplet formation

    Emulsions

    • Dispersions of small globule-shaped liquid droplets within a liquid where the two are immiscible
    • Thermodynamically unstable
      • Require emulsifiers to stabilize
    • Suitable for topical, oral, and parenteral delivery

    Emulsion Types

    • Oil-in-water (O/W)

      • Oil droplets dispersed in water
      • Oil is the internal phase, water is the external phase

    • Water-in-oil (W/O)

      • Water droplets dispersed in oil
      • Water is the internal phase, oil is the external phase

    Emulsifiers

    • Hydrophilic–lipophilic balance (HLB)

      • Reflects the balance of hydrophilic and lipophilic moieties in a surfactant molecule
      • Higher HLB values indicate a greater hydrophilic character.

    • Bancroft’s rule:

      • The phase in which the emulsifier is more soluble constitutes the continuous phase
      • Water-soluble surfactants tend to form O/W emulsions, while oil-soluble surfactants form W/O emulsions.

    Factors Affecting Emulsion Type

    • Emulsifier:

      • Some emulsifiers form either O/W or W/O emulsions based on HLB
      • Others form only one type
      • Bancroft's rule applies.

    • Phase-volume ratio:

      • The liquid with the larger volume is typically the external phase

    • Order of mixing:

      • Can impact emulsion type

    Purpose of Emulsions & Emulsification

    • Create stable, homogenous mixtures of two immiscible liquids
    • O/W emulsions offer a palatable way to administer oil
    • Topically applied emulsions (creams) can be O/W or W/O
    • Allow for the uniform mixing of oil-soluble agents.
    • Emulsions administered orally or intravenously are mainly O/W, while topical emulsions are often W/O or O/W.

    Features of a "Good" Emulsion

    • Stable
    • Even consistency
    • Suitable viscosity for easy removal from the container
    • Small droplet size with low variability
    • Slow droplet aggregation with easy redispersion upon shaking

    Rheology of Emulsions

    • Rheology studies the deformation and flow of matter.

    • Emulsion rheology is influenced by factors like:

      • Viscosity of the continuous phase
      • Phase-volume ratio
      • Emulsifier
      • Droplet size and distribution

    • Emulsions generally exhibit non-Newtonian rheology

    Preparation of Emulsions

    • Depends on the desired emulsion type and appropriate emulsifier.

    • Three main types of emulsifiers:

      • Hydrophilic colloids
      • Finely divided solid particles
      • Surfactants

    Expected Qualities of an Emulsifier

    • Compatibility with ingredients, not affecting product stability or efficacy
    • Resistance to deterioration in the preparation
    • Non-toxic
    • Minimal color, odor, and taste
    • Ability to form and maintain the desired emulsion type over the product's shelf life.

    Hydrophilic Colloids

    • Water-soluble polymers
    • Tend to form O/W emulsions
    • Form multi-molecular films around dispersed oil droplets
    • Don't significantly lower surface tension
    • Increase viscosity of the dispersion medium.
    • Usage in pharmaceuticals has declined, but they remain common in food applications.

    Hydrophilic Colloids

    • Natural (carbohydrate-based):

      • Acacia, tragacanth, alginates, pectin, agar, carageenan

    • Natural (protein-based):

      • Casein, gelatin -Semi-synthetic:

      • Methylcellulose, sodium carboxymethylcellulose

    • Synthetic:

      • Carbopol (acrylic acid derivative).

    Finely Divided Solids

    • Adsorbed at the interface between two immiscible liquids

    • Form a film around dispersed globules

      • O/W emulsions are formed by powders preferentially wetted by water
      • W/O emulsions are formed by powders preferentially wetted by oil

    • Examples:

      • Bentonite (O/W and W/O for external use)
      • Magnesium hydroxide (O/W for internal use).

    Bentonite

    • Primarily composed of crystalline clay minerals, specifically hydrous aluminum silicates
    • Contains iron, magnesium, and either sodium or calcium.### Surfactants
    • Surfactants are compounds that adsorb at interfaces, reducing interfacial tension.
    • This occurs by forming a coherent monolayer around dispersed droplets, preventing coalescence.
    • Ideally, the film should be flexible, allowing for deformation without breaking.
    • Surfactants can also carry a charge, impacting their properties.

    Emulsifiers

    • Combinations of emulsifiers are often used for optimal performance.
    • A hydrophilic agent in the aqueous phase and a hydrophobic agent in the oil phase work together to create a stable emulsion.
    • The type of emulsion (oil-in-water or water-in-oil) depends on the emulsifier's properties.
    • Each emulsifier has a hydrophilic and a lipophilic portion, categorized by their HLB (Hydrophilic-Lipophilic Balance).
    • HLB values between 4-6 favor water-in-oil emulsions, while 8-18 favor oil-in-water emulsions.
    • Common examples of emulsifiers include Tweens and Spans.

    Surfactant Action

    • Surfactants reduce interfacial tension by orienting at the interface, separating immiscible phases.
    • Their hydrophilic portion stays in the aqueous phase, while their hydrophobic portion stays in the non-aqueous phase.
    • Above the critical micelle concentration (CMC), surfactants form micelles, which act as solubilizing agents.

    4 Major Classes of Surfactants

    • Anionic Surfactants
      • Hydrophilic portion carries a negative charge.
      • Examples: Soap (sodium salt of fatty acids) and Sodium lauryl sulfate.
      • Commonly used in detergents, shampoos, and cleansers.
      • Primarily topical due to oral toxicity.
    • Cationic Surfactants
      • Cationic portion provides emulsifying properties.
      • Examples: Benzalkonium chlorides.
      • Possess disinfectant and preservative properties.
      • Primarily topical and ophthalmic due to oral toxicity.
      • Incompatible with anionic surfactants, but often used with non-ionic surfactants for improved results.
    • Amphoteric Surfactants
      • Hydrophilic portion carries both positive and negative charges.
      • Can act as anionic, non-ionic, or cationic depending on the solution's pH.
      • Rarely used as the sole surfactant.
      • Example: Sodium lauroylsarcosinate.
    • Non-ionic Surfactants
      • Hydrophilic portion has no charge.
      • Examples: Tweens and Spans (explained earlier), Cremophores (glycerol-PEG-fatty acid esters) derived from castor oil.

    Naturally Occurring Surfactants

    • Derived from plant and animal sources, often used in compounding.
    • Disadvantages include batch-to-batch variability and susceptibility to microbial growth.
    • Examples: Beeswax, wool fat (lanolin), wool alcohols, acacia, and other plant gums.

    Important Biological Surfactants

    • Bile Salts:
      • Synthesized in the liver and secreted into the gut.
      • Highly surface active, crucial for fat digestion and absorption.
      • Disperse fat, allowing lipase to access it effectively.
      • Increase dissolution rates of poorly water-soluble drugs, improving absorption and bioavailability.
    • Phospholipids:
      • Building blocks of biological membranes.
      • Found in the alveolar lining of the lungs, preventing air sac collapse and aiding in lung inflation.
      • Deficiency causes respiratory distress syndrome in newborns, often treated with artificial or animal-derived lung surfactants.
      • Present in the tear film, ensuring spread over the cornea and increasing wetting of the eye surface.
      • Deficiency contributes to dry eye syndrome, treated with artificial tear fluids containing phospholipid surfactants.

    HLB System

    • Hydrophilic-Lipophilic Balance is a numerical scale (0 - 50) that measures the balance between hydrophilicity and lipophilicity in surfactants.
    • Low HLB values (0-3) indicate lipophilic surfactants, while high values (10-18) indicate hydrophilic surfactants.
    • HLB values dictate surfactant application:
      • 0-3: Antifoaming agents.
      • 4-6: W/O emulsifying agents.
      • 7-9: Wetting agents.
      • 8-18: O/W emulsifying agents.
      • 13-15: Detergents.
      • 10-18: Solubilizing agents.
    • The Bancroft Rule states that the emulsifier is more soluble in the continuous phase of an emulsion.
    • Using a blend of surfactants, the HLB values are additive based on their proportions in the mixture.

    HLB Applications

    • Antifoaming agents (HLB 1-3):
      • Reduce surface tension of gas bubbles, causing collapse and promoting coalescence.
      • Dissipate foams, which are often undesirable in liquid preparations.
    • W/O emulsifying agents (HLB 4-6):
      • Reduce interfacial tension between water and oil, creating stable water-in-oil emulsions.
      • Example: Span 60.
    • Wetting agents (HLB 7-9):
      • Lower the contact angle between a surface and a liquid, enabling water to displace air and wet the surface efficiently.
      • Example: Bile salts.
    • O/W emulsifying agents (HLB 8-18):
      • Reduce interfacial tension between oil and water, creating stable oil-in-water emulsions.
      • Example: Tween 80.
    • Detergents (HLB 13-15):
      • Facilitate the mixing of hydrophobic compounds (like oil or grease) with water.
      • Reduce surface tension, aiding in wetting the surface and emulsifying dirt/grease/oil.
      • Example: Sodium lauryl sulfate.
    • Solubilizing agents (HLB 10-18):
      • Increase the solubility of poorly soluble materials in the formulation.
      • At the CMC, surfactants form micelles where the lipophilic core encapsulates poorly soluble drugs, allowing them to dissolve in water.
    • Commonly Used Surfactants:
      • Spans: Sorbitan esters.
      • Tweens: Polyoxyethylene sorbitan fatty acid esters.
      • They are often used in combination, usually at 2% of the total formulation.

    HLB for Oils and Oil-like Substances:

    • Oil phases also have HLB values, which influence the choice of emulsifier for a stable emulsion.
    • For a stable emulsion, the emulsifier's HLB should match the oil phase HLB, depending on the desired emulsion type (w/o or o/w).
    • HLB values for blended emulsifiers are additive based on their proportions in the mixture.

    Practice Problem - Emulsion Formulation

    • You are tasked with formulating an emulsion containing cetyl alcohol, white wax, anhydrous lanolin, an emulsifier, glycerin, and distilled water.
    • To determine the type of emulsion (O/W or W/O), the HLB of the oil phase is calculated.
    • The HLB values of the individual components are multiplied by their respective weights, and the results are summed.
    • This sum is then divided by the total weight of the oil phase components to yield the overall HLB of the oil phase.

    The provided text does not offer a solution to the practice problem but sets up the calculation process for the HLB required for the oil phase of the emulsion.

    Emulsion Preparation

    • Emulsions can be prepared on small or large scales using various equipment.
    • Small-scale preparation involves tools like mortar and pestle, a beaker, a blender, a hand homogenizer, and a prescription bottle.
    • Large-scale preparation utilizes mixing tanks with high-speed impellers, followed by processing in a colloid mill or a large homogenizer.

    Emulsification Using Acacia Gum

    • Acacia gum, a natural emulsifier obtained from acacia trees, stabilizes oil-in-water emulsions.

    • Two main methods are used:

      • Continental or dry gum method: involves mixing acacia gum with oil and then adding water gradually.
      • English or wet gum method: involves mixing acacia gum with water first and then adding oil gradually.### Emulsification - Dry Gum vs Wet Gum Method

    • The Dry Gum Method involves dispersing acacia in oil, adding part of the water at once with rapid trituration, and then slowly adding the rest of the water.

    • This method is faster and more reliable than the Wet Gum Method.

    • The Wet Gum Method involves dispersing acacia in water (to form a mucilage), slowly adding the oil, and then adding the remaining water.

    • This method is slower and less reliable than the Dry Gum Method, but it is useful when the emulsifier is available as a solution or needs to be dissolved prior to use.

    Emulsification - Surfactants

    • Surfactants are selected based on their HLB (Hydrophilic-Lipophilic Balance) value.
    • Different emulsifiers can be blended.
    • Tweens and Spans are commonly used surfactants.

    Emulsification of Surfactants - Methods

    • Bottle or Forbes Method: suitable for volatile oils and low viscosity oils. Ingredients are shaken together in a closed bottle.
    • Beaker Method: uses heat as the primary energy source for emulsification. Oil and water phases are heated separately, then mixed.

    In Situ Soap Emulsions

    • Calcium soaps (hard soaps): form W/O emulsions when olive oil and lime water (calcium hydroxide solution) are mixed.
    • Soft soaps: are usually O/W emulsions. They are water soluble and dispersible and are made with salts of fatty acids (stearic, palmitic, lauric, and oleic acids) and a univalent positive ion (K+, Na+, NH4+).

    Adding Drugs to Emulsions

    • Drugs should be incorporated during emulsion formation.
    • Oleaginous materials are added to the oil phase and aqueous materials to the water phase.
    • Thermolabile drugs should be added to the emulsion after it has cooled.

    Emulsion Type - O/W vs W/O

    • O/W emulsions can be diluted with water, conduct electricity, and allow water-soluble dyes to disperse uniformly.
    • W/O emulsions are not easily diluted with water, do not conduct electricity, and inhibit uniform dispersion of water-soluble dyes.

    Physical Stability of Emulsions

    • Optimal phase volume ratio: 50:50.
    • Interface film properties: a tough, elastic film that forms readily during emulsification is crucial.
    • Electrostatic repulsion: stabilizes emulsions by repelling droplets.

    Emulsion Instability

    • Creaming: the separation of an emulsion into regions of different internal phase concentrations. Can be reversed, unless coalescence occurs.
    • Coalescence (Cracking or Breaking): irreversible process where the emulsifying agent film surrounding oil droplets is broken.
    • Phase Inversion: conversion to the opposite emulsion type. Can be triggered by temperature extremes (freezing or exposure to excessive heat).

    Preservation of Emulsions

    • Preservatives should be partitioned between the oil and water phases.
    • Bacteria primarily grow in the water phase.
    • Fungistatic preservatives are recommended for O/W emulsions.
    • Common preservatives include methyl and propyl paraben, and alcohol (at 12-15%). Avoid alcohol with hydrocolloid emulsifiers.

    Selected Commercially Available Products

    • Oral emulsions: BioGenesis Omega Emulsion Lemon, Microlipid®, Liquigen®
    • Ophthalmic emulsion: Restasis® (cyclosporine)
    • Injectable emulsions: Diprivan® (propofol), Cleviprex® (clevidipine butyrate), Intravenous Fat Emulsions (IVFE)

    Microemulsions

    • Contain large, swollen micelles holding the internal phase.
    • Appear transparent.
    • Internal phase droplets are 10-200 nm in diameter.
    • Used for enhanced drug absorption, topical delivery, cancer chemotherapy, transplant medication, and cosmetics.

    Commercially Available Microemulsions

    • PropoClear® (propofol): veterinary use.
    • Neoral® (cyclosporine): forms microemulsion immediately in aqueous environments.

    Suspensions

    • Systems with finely divided solid particles dispersed throughout a vehicle.
    • Administered via multiple routes (oral, topical, otic, ophthalmic, rectal, IM, SC) but NEVER by IV!

    Reasons for Preparing Suspensions

    • Chemical stability: for drugs unstable in solution.
    • Taste masking.
    • Insolubility.

    Features of a Good Suspension

    • Pours readily and evenly.
    • Small and uniformly sized particles (typically 1-5 microns).
    • Slow settling and easy redispersion.
    • No caking of settled particles.

    Flocculation vs Deflocculation

    • Flocculation: loose aggregates of particles held together by weak forces. Results in rapid sedimentation with clear supernatant.
    • Deflocculation: particles are dispersed individually, resulting in slower sedimentation and a cloudy supernatant.

    Sedimentation Volume

    • The ratio of the volume of sediment to the initial volume of the suspension.
    • Can range from 0 to 1 (ideal suspension has F=1 with no sedimentation or caking).
    • F can exceed 1 if flocs are bulky.

    Degree of Flocculation

    • The ratio of the sedimentation volume (F) to the sedimentation volume of a completely deflocculated suspension (F∞).

    Velocity of Sedimentation

    • Explained by Stokes' Law.
    • Factors affecting sedimentation velocity:
      • Particle diameter (directly proportional)
      • Density difference between dispersed phase and medium (directly proportional)
      • Viscosity of the medium (inversely proportional).

    Conclusions from Stokes' Law

    • Larger particles, denser dispersed phases settle more quickly.
    • Viscosity of the medium affects settling rate.
    • Controlled settling can be achieved by particle size reduction, increasing viscosity, or preventing aggregation.

    Suspensions

    • Deflocculated systems are ideal, but they can be too viscous to pour.
    • Flocculated systems with controlled sedimentation are a compromise. They allow for easy redispersion and are more visually appealing.
    • The sedimentation rate of a suspension can be calculated using the Stokes' Law equation.
    • Wetting agents are used to promote uniform dispersion of drug particles in the dispersion medium.
    • Suspending agents in the vehicle (continuous phase) slow down sedimentation of dispersed particles.
    • Flocculating agents promote aggregation of dispersed particles, maximizing sedimentation volume and preventing the formation of a dense cake at the bottom of the container.
    • Examples of flocculating agents include electrolytes, polymers, clays, and surfactants.
    • Oral suspension dosage forms often contain: active ingredient, wetting agent, dispersion medium, suspending agent, sweetener, flavor, flocculating agent, and preservative.
    • Particle size reduction is important for preparing suspensions.
    • Suspensions are typically packaged in light-resistant, airtight containers and stored in the refrigerator unless stability data suggests otherwise.
    • A "Shake Well Before Using" or "Shake Well and Keep in the Refrigerator" label is required for suspensions.

    Polymorphism in Suspensions

    • Polymorphism can affect the physical stability of suspensions.
    • Only one polymorphic form is typically stable.
    • Meta-stable forms may convert to the stable form over time.
    • This conversion can affect properties such as solubility, dissolution rate, and bioavailability.

    Gels

    • Gels are semi-solid systems consisting of a dispersion of small inorganic particles or large organic molecules in a liquid.
    • Both single-phase and two-phase gels are colloidal dispersions.
    • Gels are semi-rigid systems in which the movement of the dispersing medium is restricted by a network of dispersed particles or macromolecules.
    • Syneresis is the expulsion of liquid from a gel, often considered an instability.
    • Imbibition is the displacement of one fluid by another immiscible fluid.
    • Swelling occurs during gel formation as elastic forces increase in macromolecules.

    Single-Phase Gels (Mucilages)

    • Single-phase gels contain soluble organic macromolecules (linear or branched polymers).
    • The continuous phase can be aqueous, hydroalcoholic, or non-aqueous.
    • In molecular dispersions, no apparent boundaries exist between dispersed molecules and the liquid.
    • Examples of single-phase gels include tragacanth, methylcellulose, and carbomer gels.

    Two-Phase Gels

    • Two-phase gels consist of a network of small, discrete particles in a liquid.
    • These gels are often thixotropic, meaning they are semi-solid at rest but liquefy when shaken.
    • Magmas and milks are subsets of two-phase gels.
    • Examples of two-phase gels include aluminum hydroxide gel and bentonite magma.
    • Magmas are suspensions of clays in water that exhibit thixotropic rheological behavior.
    • Milks are suspensions in aqueous vehicles intended for oral and topical administration.

    Multi-phase (dispersed) systems

    • Pharmaceutical systems consist of particulate matter dispersed throughout a continuous phase
    • Include Suspensions, Emulsions, Gels, and Magmas
    • Properties are often related to the presence of a boundary between two phases (the interface)

    Dispersed Systems

    • Preparations consisting of solid particulate matter or a dispersed phase distributed throughout a dispersion medium or continuous phase (also “coarse dispersions”)
    • Heterogeneous systems
    • Must shake well
    • Opaque appearance (but see next slide)
    • Increased viscosity
    • Non-Newtonian flow

    Advantages of dispersed systems

    • Similar to advantages of other oral liquid dosage forms
    • Easy to swallow
    • Flexible dosing
    • Easy to administer
    • Rapid onset of action
    • Faster than solid dosage forms
    • Modify the onset of action
    • Extended or delayed release possible

    Disadvantages of dispersed systems

    • Non-homogenous
    • Tendency to separate (need Shake Well label)
    • Bulkier than solid dosage forms
    • Taste may be an issue
    • Certain drugs are not stable in liquid dosage forms
    • Dose accuracy
    • Spills
    • Incorrect measuring device

    Additional Excipients Present in Multi-Phase Liquids

    • Emulsifying agents
      • Facilitates the dispersion of two immiscible liquids and stabilizes it
      • Examples: Polysorbate (Tween) 80, Span 80, Acacia
    • Encapsulating or solubilizing agents
      • Promote and maintain dispersion of finely subdivided droplets of liquid in a vehicle in which it is immiscible
      • Examples: Acacia, Cetomacrogol, Cetyl alcohol, Glyceryl monostearate, Sorbitan monooleate

    Surfactant (Surface active agent)

    • Substances that adsorb onto the interfaces between phases to reduce interfacial tension
    • May be used as detergents, or emulsifying agents
    • Examples: Benzalkonium chloride, Polysorbate 80, Sodium lauryl sulfate

    Levigating Agent

    • Liquid used as an intervening agent to reduce the particle size of a powder by grinding, usually in a mortar
    • Liquid used to ensure complete wetting/even dispersion of a solid ingredient into a liquid or semisolid product
    • Displaces the film of air that exists on the surface of dry powders
    • Examples: Mineral oil, Glycerin, Propylene glycol

    Suspending Agent

    • Viscosity-increasing agent used to reduce sedimentation rate of particles in a vehicle in which they are not soluble
    • Examples: Bentonite, Carbomers (Carbopol®), Cellulose derivatives (MC, HEC, HPMC, HPC), Tragacanth, Polyvinyl alcohol

    Physical Pharmacy and Problems associated with Multi-phase Systems

    • Wetting of solid particles
      • Most important for suspensions
      • Some solids float on surface when sprinkled on water (or other liquid)
      • Talc
      • Charcoal
      • “Wetting” = Ability of a liquid to displace air and to spread over the entire surface of solid particles
      • Particles need to be “wetted” in order to be immersed in the liquid
      • Liquid must displace air and spread over the surface of the solid

    Wetting of solid particles

    • How well solids are wetted is described by the contact angle (θ)
      • Depends on the nature of the liquid and the nature of the solid surface (hydrophilic….hydrophobic)

    Wetting of solid particles

    • A drop of water is placed on a flat, smooth, horizontal surface
    • The drop behaves in one of the fashions shown below:
      • Complete (absolute) wetting: Contact angle is 0º
      • Readily wetted solids: 0º < contact angle < 90º
      • Poorly wetted solids: 90º < contact angle < 180º
      • Non-wetted: Contact angle is 180º

    Wetting of solid particles

    • Problems caused by insufficient wetting:
      1. Cannot mix powder with liquids to form suspensions
      2. Ingredients from tablets and capsules are not wetted by GI fluids causing dissolution problems
      • Incomplete absorption
      • Problems can be increased by too much hydrophobic lubricant in tablets and capsules
      • Wetting agents can be added to increase interfacial contact

    Particle aggregation / caking

    • Particle aggregation:
      • Small particles are attracted to each other → form larger and heavier particles → fall out of suspension. But resuspendable
    • Caking:
      • Form solid mass at bottom of bottle
      • Agglomerated particles are difficult to resuspend
    • Can be prevented by development (adding) of surface charge
      1. Ionization of surface groups: Carboxylic acid groups, Amines
      2. Adsorption of electrolytes from the solution onto particle surface
      3. Adsorption of charged surfactant molecules from the solution

    Particle aggregation / caking: Surface charge

    • Importance of Zeta (ζ) potential
      • Or “electrokinetic potential”

    Zeta (ζ) potential

    • Controls the degree of repulsion between adjacent, similarly charged, dispersed particles
      • The higher = The more stable the suspension
    • If Zeta (ζ) potential is below a threshold value:
      • Attractive forces exceed repulsive forces
      • Particles aggregate
      • Suspension becomes unstable

    Interfacial phenomena

    • Surface: Boundary between two phases, where one of them is strictly gas
    • Interface: Boundary between two immiscible phases
    • Every surface is an interface too!
    • Surface tension:
      • Describes the interface between liquids and gas
      • Unbalanced molecular cohesive forces exist at or near the surface
      • Net attractive force is towards the bulk of the liquid
      • Surface tends to contract and resemble a stretched elastic membrane

    Surface tension

    • Each molecule forms a bond with the ones in its vicinity.
    • At the surface the outmost layer of molecules has fewer molecules to “cling to”, therefore “compensates” by establishing stronger bonds with its neighbors, this leading to the formation of the surface tension.

    Interfacial tension

    • Interfacial tension = Force of attraction between the molecules at the interface of two fluids.
    • At the air/liquid interface, interfacial tension is referred to as surface tension.
    • Interfacial tension = Tension between two immiscible liquids
    • Interfacial tension is the force acting between two different liquids.
    • Higher interfacial tension: Both liquids tend to separate into two phases. Each molecule of one liquid prefers to stay with the other molecules of that same liquid
    • Surface and interfacial tension are reduced as the temperature increases
    • Addition of certain solutes reduces the surface tension (surfactants = surface active agents… more details later)

    Interfacial tension (γs)

    • Correlates to the amount of energy (“E”) required to increase the interfacial (contact) area (“A”) between two immiscible liquids
      • ΔE = γs ΔA

    Emulsions

    • A dispersion in which the dispersed phase is composed of small globules of liquid distributed throughout a vehicle in which it is immiscible
    • Dispersed phase = internal phase, discontinuous phase
    • Dispersion medium = external phase, continuous phase
    • Emulsions are thermodynamically unstable
    • Thermodynamic instability means a system exists that is not at equilibrium. Require an emulsifying agent to be stable
    • Suitable for topical, oral, and parenteral delivery

    Emulsions

    • Emulsions consist of:
      • Small droplets of water dispersed in oil (W/O), or
    • Small droplets of oil dispersed in water (O/W)
    • Contact area between water and oil is very large
    • More energy for increasing A…
    • Remember: ΔE = γs ΔA
      • therefore energetically unstable
    • Cohesive forces among molecules of the same phase will try to “bring them back together”
      • Water prefers to stay with water
      • Oil prefers to stay with oil

    Emulsions

    • Liquid 1
    • Liquid 2
    • Dispersed phase of Liquid 1 (as droplets) without emulsifier
    • Dispersion medium is Liquid 2
    • Coalescence of dispersed phase without emulsifier
    • Dispersion medium
    • Stable dispersed phase (as droplets) of Liquid 1 with an emulsifier (Blue outer ring)
    • Dispersion medium

    Emulsion Type

    • Oil-in-water emulsions (O/W)
    • Oil dispersed in water: Oil is the internal/dispersed/ discontinuous phase
    • Water-in-oil emulsions (W/O)
    • Water dispersed in oil: Water is the internal/dispersed/discontinuous phase

    Two definitions needed for next slide

    • “HLB”: Hydrophilic–lipophilic balance:
      • Balance of the size and strength of the hydrophilic and lipophilic moieties of a surfactant molecule (details later)
    • “Bancroft’s Rule”: The phase in which an emulsifier is more soluble constitutes the continuous phase. More water-soluble surfactants tend to give oil-in-water emulsions. More oil-soluble surfactants give water-in-oil emulsions.

    Factors that affect the emulsion type

    • Emulsifier
    • Some emulsifiers can form either type of emulsion
    • Depends on HLB the ingredients
    • Other emulsifiers form only O/W or only W/O
    • Bancroft’s Rule: the phase in which the emulsifier is more soluble = external phase
    • Phase-volume ratio
    • Larger volume liquid is almost always the external phase
    • Order of mixing
      • May have some impact on emulsion type

    Purpose of emulsions and emulsification

    • To prepare relatively stable and homogenous mixtures of two immiscible liquids
    • O/W emulsions are a palatable way of administering distasteful oil
    • Emulsions to be applied to the skin can be prepared as O/W or W/O emulsion.
    • Medications that are irritating to the skin can be administered as an internal phase of a topical emulsion.
    • W/O emulsions allow for uniform mixing of oil-soluble agents
    • Emulsions that are administered orally or by IV route are primarily O/W type, while topically applied emulsions (creams) are W/O or O/W type.

    Features of a “good” emulsion

    • Emulsion should be stable.
    • The emulsion should be of an even consistency
    • The emulsion should be of a viscosity such that it can be readily removed from its container and used (e.g.lotion should pour/pump, cream should come out of tube or jar easily)
    • Particle size of the droplets should be as small as possible and remain fairly constant.
    • Droplets should aggregate slowly and be easily re-dispersed when the container is shaken.

    Rheology of emulsions

    • Rheology: Branch of physics that deals with the deformation and flow of matter.
    • Factors that affect rheology:
      • Viscosity of continuous phase
      • Phase-volume ratio
      • Emulsifier
      • Droplet size and size distribution
    • Rheology of emulsions in general is Non-Newtonian

    Preparation of emulsions

    • Preparation depends on:
    • Type of emulsion (we want to prepare)
    • Emulsifier (which in turn depends on type of emulsion)
    • Three types of emulsifiers (details in following slides):
    • Hydrophilic colloids
    • Finely divided solid particles
    • Surfactants

    Expected qualities of an emulsifier

    • Compatible
      • Should not affect the stability and efficacy of the product
    • Should not deteriorate in the preparation
    • Non-toxic
    • Possess little or no color, odor, taste
    • Capable of forming desired emulsion, and maintaining it for the shelf life of the preparation

    1) Hydrophilic colloids

    • Water soluble polymers
    • Tend to form O/W emulsions
    • Form multi-molecular film around the dispersed droplets of oil
    • Do not cause an appreciable lowering in the surface tension
    • Increase the viscosity of the dispersion medium
    • The use of natural hydrophilic colloids in pharmaceuticals has declined in recent years
    • Still commonly used in the food industry

    Hydrophilic colloids

    • Natural (carbohydrate-based):
      • Acacia, tragacanth, alginates, pectin, agar, carageenan
    • Natural (protein-based):
      • Casein, gelatin
    • Semi-synthetic:
      • Methylcellulose, sodium carboxymethylcellulose
    • Synthetic:
      • Carbopol (derivative of acrylic acid)

    2) Finely divided solids

    • Adsorbed at the interface between the two immiscible liquid phases
    • Form a film of solid particles around the dispersed globules
      • O/W emulsions formed by powders that are preferentially wetted by water
      • W/O emulsions formed by powders that are preferentially wetted by oil
    • Examples:
      • Bentonite (O/W and W/O for external use)
      • Magnesium hydroxide (O/W for internal use)

    Bentonite

    • Consists chiefly of crystalline clay minerals, which are hydrous aluminum silicates containing iron and magnesium as well as either sodium or calcium.

    Surfactants

    • Surfactants reduce interfacial tension
    • Surfactants form monomolecular films at oil-water interfaces
    • Surfactants prevent droplet coalescence
    • Surfactants have hydrophilic and lipophilic portions
    • Surfactants are categorized based on their HLB (Hydrophilic-Lipophilic Balance)
    • Surfactants with an HLB of 4-6 produce W/O emulsions
    • Surfactants with an HLB of 8-18 produce O/W emulsions

    Surfactant Examples

    • Tweens and Spans are fatty acid esters of sugar alcohol (sorbitan) derivatives
    • Span 80 is a surfactant
    • Tween 20 is a surfactant

    Surfactant Properties

    • Surfactants decrease interfacial tension
    • Surfactants separate immiscible phases
    • Surfactants form micelles
    • Surfactants have polar and non-polar characteristics
    • Surfactants adsorb at interfaces

    Surfactant Classes

    • Anionic surfactants have a negative charge
    • Anionic surfactants are commonly used as detergents, shampoos, and body cleansers
    • Anionic surfactants are inexpensive
    • Anionic surfactants have oral toxicity
    • Cationic surfactants have a positive charge
    • Cationic surfactants have disinfectant and preservative properties
    • Cationic surfactants have oral toxicity
    • Cationic surfactants are incompatible with anionic surfactants
    • Amphoteric surfactants have both positive and negative charges
    • Amphoteric surfactants can behave as anionic, non-ionic, or cationic species depending on pH
    • Non-ionic surfactants have no charge
    • Non-ionic surfactants are not electrolytes

    Naturally Occurring Surfactants

    • Naturally occurring surfactants are derived from plant and animal sources
    • Naturally occurring surfactants have batch-to-batch variability
    • Naturally occurring surfactants are susceptible to bacteria and mold growth
    • Naturally occurring surfactants are used in compounding
    • Beeswax is a naturally occurring surfactant
    • Wool fat (lanolin) is a naturally occurring surfactant
    • Wool alcohols are naturally occurring surfactants
    • Acacia and other plant gums are naturally occurring surfactants

    Important Biological Surfactants

    • Bile salts are synthesized in the liver and secreted into the gut
    • Bile salts are highly surface active
    • Bile salts enhance fat digestion and absorption
    • Bile salts increase the dissolution rate of poorly water-soluble drugs
    • Phospholipids are building blocks of biological membranes
    • Phospholipids are important in the alveolar lining of lungs
    • Phospholipids are important in the tear film of the eye

    HLB System

    • Hydrophilic-Lipophilic Balance (HLB) ranges from 0-50
    • HLB values indicate surfactant balance between hydrophilicity and lipophilicity
    • Griffin’s Method calculates HLB based on lipophilic portion molecular mass and total molecular mass
    • Davies’ Method calculates HLB considering the different degree of hydrophilicity of hydrophilic groups

    HLB Application

    • HLB values determine surfactant application
    • Anti-foaming agents have an HLB of 0-3
    • W/O emulsifying agents have an HLB of 4-6
    • Wetting agents have an HLB of 7-9
    • O/W emulsifying agents have an HLB of 8-18
    • Detergents have an HLB of 13-15
    • Solubilizing agents have an HLB of 10-18

    HLB in Emulsions

    • The HLB of a surfactant should be similar to the oil phase for a stable emulsion
    • HLB values are additive when using a blend of surfactants

    Example HLB Values for Emulsions

    • Stearic acid has an HLB of 6 for W/O emulsions and 15 for O/W emulsions
    • Cetyl alcohol has an HLB of 15 for O/W emulsions
    • Stearyl alcohol has an HLB of 14 for O/W emulsions
    • Anhydrous lanolin has an HLB of 8 for W/O emulsions and 10 for O/W emulsions
    • Cottonseed oil has an HLB of 5 for W/O emulsions and 10 for O/W emulsions
    • Mineral oil has an HLB of 5 for W/O emulsions and 12 for O/W emulsions
    • Petrolatum has an HLB of 5 for W/O emulsions and 12 for O/W emulsions
    • White wax (Beeswax) has an HLB of 4 for W/O emulsions and 12 for O/W emulsions

    HLB Practice Problem

    • The practice problem involves calculating the HLB of an oil phase and the amounts of emulsifiers needed for an emulsion
    • The HLB is calculated as a weighted average of the HLBs of the oil phase ingredients
    • The amount of each emulsifier is calculated using a system of equations or the alligation method
    • The goal of the problem is to create a stable O/W emulsion

    Emulsion Preparation

    • Equipment for small-scale emulsion preparation includes a mortar and pestle, a beaker, a blender, a hand homogenizer, and a prescription bottle
    • Equipment for large-scale emulsion preparation includes large mixing tanks, a high-speed impeller, a colloid mill, and a homogenizer

    Acacia Emulsions

    • Acacia is a natural emulsifier obtained from acacia trees
    • Acacia is used to stabilize oil-in-water emulsions
    • Two major methods for preparing emulsions with acacia include the continental or dry gum method.

    Emulsification

    • Acacia or similar agents can be used to form emulsions
    • Ratio for fixed oils is 4 parts fixed oil : 2 parts water : 1 part emulsifier
    • Ratio for volatile oils is 2 parts volatile oil : 2 parts water : 1 part emulsifier

    Continental or Dry Gum Method

    • Acacia is dispersed thoroughly in oil
    • Part of water is added at once with rapid trituration
    • Trituration is continued using a spiral motion until a snapping sound is heard, indicating a thick primary emulsion has formed.
    • The rest of the water phase is then slowly added with trituration

    English or Wet Gum Method

    • The same proportions as the dry gum method but mixed in a different order
    • A mucilage is formed by dispersing acacia thoroughly in 2 parts water
    • Oil is added slowly with rapid trituration
    • Trituration continues at high speed and the rest of the water is added slowly with trituration
    • Slower and less reliable than the dry gum method
    • Useful when the emulsifier is only available as a solution or must be dissolved before using

    Selecting Emulsifiers

    • HLB values are algebraically additive
    • Blends of emulsifiers are possible
    • Tweens and Spans are most commonly used

    Emulsification Using Surfactants

    • Bottle or Forbes Method:
      • Ingredients are shaken together in a closed prescription bottle
      • Suitable for volatile oils and oils with low viscosity
      • Not suitable for viscous oils
    • Beaker Method:
      • Primary energy source is thermal rather than mechanical
      • Oil and water phases are heated separately
      • Requires a high enough temperature to melt solid components but a low enough temperature to not scorch oil-phase ingredients or boil water
      • Not suitable for thermolabile drugs
      • Once phases are similar in temperature, the smaller-volume phase is added to the larger-volume phase and mixed

    In Situ Soap Emulsions

    • Prepared by beaker or bottle methods
    • Calcium soaps ("hard soaps")
      • W/O emulsions
      • Equal amounts of olive oil (oleic acid) + lime water (calcium hydroxide solution)
      • May need a little excess olive oil to ensure a homogenous emulsion
      • Addition of acid can destroy the emulsion because it shifts the equilibrium
    • Soft soaps:
      • Usually O/W emulsions
      • Water-soluble and water dispersible
      • Salts of fatty acids with a univalent positive ion (K+, Na+, NH4+)
      • Give emulsions with a basic pH
      • Unsuitable for internal use

    Addition of Drugs to Emulsions

    • Best to incorporate the drug during emulsion formation
    • Oleaginous materials should be added to the oil phase
    • Aqueous materials should be added to the water phase
    • For thermolabile drugs added to emulsions formed using the beaker method, wait until the emulsion has cooled

    Emulsion Type: O/W vs W/O

    • O/W emulsions
      • Can be diluted with water
      • Water-soluble dye will diffuse uniformly
      • Conducts electricity
    • W/O emulsions:
      • Cannot be easily diluted with water
      • Water-soluble dye will not diffuse uniformly
      • Will not conduct electricity

    Physical Stability of Emulsions

    • Optimum phase volume ratio is 50:50
    • Properties of the interfacial film have the greatest influence on stability
    • Emulsions are stabilized by electrostatic repulsion between droplets

    Emulsion Instability

    • Creaming:
      • Separation of an emulsion into two regions, one with more of the internal phase
      • E.g. fat globules rising to the top
      • Less likely if densities of the two phases are similar
      • Less likely if the external phase is very viscous
      • Storing in the refrigerator increases viscosity and slows creaming
      • Reversible process, but may not be aesthetically acceptable
    • Coalescence/Cracking/Breaking:
      • Irreversible
      • The film surrounding the droplets of the oil is broken
    • Phase inversion:
      • Conversion to the opposite emulsion type
      • Can be triggered by exposure to temperature extremes
      • Avoid freezing or leaving in a hot car

    Preservation of Emulsions

    • Preservative partition between the oil and water phases
    • Bacteria grow in the water phase
    • Fungistatic preservatives are recommended for O/W emulsions
    • Frequently used preservatives:
      • Methyl and propyl paraben
      • Alcohol 12-15% (do not use if emulsifier is a hydrocolloid)

    Commercially Available Products (Oral)

    • Limited commercially available oral emulsions in the US
    • Fish oil emulsions are available as supplements
      • BioGenesis Omega Emulsion Lemon
    • Microlipid:
      • Unflavored safflower oil emulsion
      • Medical food used to increase calorie content at a low volume
      • Supplies essential fatty acids
      • Mix into food or supplements
      • Can be administered via feeding tubes
    • Liquigen:
      • Unflavored emulsion containing medium chain triglycerides from palm and/or coconut oil
      • Does not supply essential fatty acids
      • For patients who cannot efficiently digest and absorb long chain fatty acids
      • Generally incorporated into foods (fruit juices)
      • Can be used in baking and cooking

    Commercially Available Products (Ophthalmic)

    • Restasis (cyclosporine)
      • Prescription emulsion eye drop
      • Helps increase the eyes' natural ability to produce tears

    Commercially Available Products (Injectable)

    • Intravenous fat emulsions (IVFE)
      • O/W emulsions used for nutrition support or as vehicles for delivery of lipid-soluble drugs
      • Commonly included in total parenteral nutrition (TPN) formulations with amino acids and dextrose
    • Dipravan (propofol injectable emulsion)
      • Sedative-hypnotic used in anesthesia and ICU sedation
    • Cleviprex (clevidipine butyrate)
      • Calcium channel blocker administered as an IV emulsion when oral blood pressure therapy is not feasible

    Microemulsions

    • Consist of large or "swollen" micelles containing the internal phase
    • Appear as clear (optically) transparent systems
    • Droplets in internal phase: 10-200 nm diameter
    • Uses:
      • More rapid and efficient absorption of drugs administered as microemulsions
      • Topical drug delivery
      • Cosmetic industry
      • Cancer chemotherapy
      • Transplant medication
    • Commercially Available Microemulsions:
      • PropoClear (propofol)
        • IV product for veterinary use only
        • Appears transparent to the naked eye
      • Neoral (cyclosporine)
        • Forms a microemulsion immediately upon contact with an aqueous environment
        • Available as an oral solution and soft gelatin capsules

    Suspensions

    • Multi-phase systems containing finely divided solid particles that are distributed somewhat uniformly throughout a vehicle
    • Routes of administration:
      • Oral
      • Topical
      • Otic
      • Ophthalmic
      • Rectal
      • IM or SC injection
    • Must never be given by IV
    • Reasons for preparing suspensions:
      • Chemical stability
      • Taste masking
      • Insolubility

    Features of a Good Suspension

    • Should pour readily and evenly
    • Particle size of the dispersed phase should be as small as possible (typically 1-5 microns) and fairly uniform
    • Particles should settle slowly and re-disperse easily after shaking
    • Settled particles should not form a cake on standing

    Flocculation and Deflocculation

    • Flocculation:
      • Formation of light fluffy aggregates of particles held together by weak Van der Waals forces
      • Flocs tend to sediment rapidly
      • Easily reversible by shaking
    • Deflocculation:
      • Particles exist in suspension as separate entities

    Sedimentation Volume

    • The ratio of the equilibrium volume of the sediment to the initial total volume of the suspension (before settling)
    • Ideal suspension has a sedimentation volume of 1, no sedimentation or caking
    • Sedimentation Volume (F) ranges from 0 to 1 but may exceed 1 if flocs are bulky

    Degree of Flocculation

    • Defined as the ratio of F to F∞ (sedimentation volume of completely deflocculated suspension)

    Velocity of Sedimentation - Stokes' Law

    • Helps understand the rate of particle movement
    • Velocity is directly proportional to particle diameter and density difference
    • Velocity is inversely proportional to the viscosity of the dispersion medium

    Conclusions from Stokes' Law

    • Larger particles fall more quickly
    • Denser particles fall more quickly (at a given vehicle density)
    • Rate of sedimentation is inversely proportional to viscosity

    Controlling Sedimentation

    • Particle size reduction
    • Increase the viscosity of the dispersion medium by using suspending agents
    • Prevent particle aggregation

    Suspensions

    • Suspensions can be deflocculated with no or minimal sedimentation, but this can lead to a highly viscous, difficult to pour, and difficult to dose product.
    • Flocculated systems with controlled slow sedimentation are a better option, as they are easier to redisperse.
    • Sedimentation rate can be calculated using Stokes' Law.
    • Wetting agents are used to promote dispersion of drug particles with the dispersion medium.
    • Suspending agents increase viscosity and slow down sedimentation.
    • Flocculating agents promote loose aggregation of suspended particles, maximizing sedimentation volume and avoiding dense caking.
    • Components of oral suspension dosage forms: active ingredient, wetting agent, dispersion medium, suspending agent, sweetener/flavor, flocculating agent, preservative.
    • To prepare a suspension: reduce particle size, wet the particles with wetting agent, add vehicle slowly.
    • Caking is one of the main causes of poor redispersion of a suspension after sedimentation.
    • Polymorphism can affect the physical stability of suspensions, as different polymorphs have different properties.
    • Suspensions are packaged in light-resistant, airtight containers, stored in the refrigerator, and should have a "Shake well before using" label.
    • Dry powders for oral suspension are reconstituted with water before use.
    • Delayed release suspensions contain enteric-coated granules that release the drug in the intestine.
    • Extended release suspensions release the drug over an extended period of time.

    Gels

    • Gels are semi-solid systems consisting of dispersions of small inorganic particles or large organic molecules enclosed and interpenetrated by a liquid.
    • Single-phase gels contain soluble organic macromolecules and are clear.
    • Two-phase gels contain a network of small, discrete particles and are turbid.
    • Two-phase gels are thixotropic, meaning they are semi-solid on standing but liquefy when shaken.
    • Gels can exhibit syneresis, the expulsion of liquid from the gel, which is considered an instability.
    • Magmas are suspensions of inorganic materials in water and have a gel-like consistency.
    • Milks are suspensions in aqueous vehicles intended for oral and topical administration.

    Excipients in Multi-phase Liquid Dosage Forms

    • Excipients contribute to the stability, physical properties, and deliverability of liquid dosage forms.
    • Categories:
      • Solvents: For dissolving the active pharmaceutical ingredient (API)
      • Viscosity-increasing agents: To increase the viscosity of the formulation, facilitating suspension or emulsion stability
      • Preservatives: To prevent microbial growth
      • Buffers: Maintain pH stability
      • Flavoring and Sweetening Agents: To improve taste and palatability
      • Coloring Agents: To improve visual appeal
      • Antioxidants: To prevent oxidation of the API or other components

    Wetting of Solids

    • Wetting refers to the ability of a liquid to spread over the surface of a solid.
    • Problem: Poor wetting can lead to:
      • Agglomeration: Particles clumping together, leading to poor dispersion.
      • Incomplete dissolution: API may not fully dissolve if the liquid cannot adequately wet the solid.
    • Improving wetting:
      • Use of wetting agents (surfactants): These agents reduce surface tension and increase the spreading of the liquid on the solid.
      • Particle size reduction: Smaller particles have a larger surface area, improving wetting.
    • Contact angle: A completely wetted solid has a contact angle of 0 degrees.

    Particle Aggregation Prevention

    • Causes of aggregation:
      • Attractive forces between particles: These include van der Waals forces, electrostatic interactions, and hydrogen bonding
      • Poor wetting: If the liquid doesn't wet the solid well, it creates conditions for aggregation.
    • Prevention:
      • Use of dispersing agents: These agents surround the particles and prevent them from sticking together.
      • Control of particle size: Smaller particles have a lower chance of aggregating.
      • Agitation during formulation: Maintaining a good level of mixing helps keep particles dispersed.

    Surface Tension & Interfacial Tension

    • Surface tension: The force per unit length that exists at the interface between a liquid and air or another gas.
    • Interfacial tension: The force per unit length that exists at the interface between two immiscible liquids.

    Emulsifying Agents

    • Emulsifying agents are substances added to an emulsion to stabilize it, preventing the two phases from separating.
    • Categories:
      • Hydrocolloids: These are large molecules that create a viscous layer around the dispersed phase (oil droplets in an oil-in-water emulsion or water droplets in a water-in-oil emulsion), preventing their coalescence. Examples include gum acacia, tragacanth gum, and alginates.
      • Finely divided particles: These particles create a physical barrier between the dispersed phase droplets, preventing coalescence. Examples include bentonite and magnesium hydroxide.
      • Surfactants: These molecules have a hydrophilic (water-loving) head and a hydrophobic (water-hating) tail. They align at the interface between the dispersed phase and the continuous phase, creating a stable interface. Examples: Sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CETAB).

    Surfactants

    • Categories:
      • Anionic: Have a negatively charged head group. Example: Sodium lauryl sulfate (SLS).
      • Cationic: Have a positively charged head group. Example: Benzalkonium chloride (BAC).
      • Nonionic: Have no charge on their head group. Example: Polyethylene glycol (PEG).
      • Zwitterionic: Have both positive and negative charges on their head group. Example: Lecithin.

    Naturally Occurring Surfactants

    • Examples:
      • Bile salts are naturally occurring surfactants in the body that help digest fats by emulsifying them in the small intestine.
      • Pulmonary surfactant is a mixture of lipids and proteins that lines the alveoli in the lungs. It reduces surface tension, preventing collapse of the alveoli during exhalation.

    Pharmaceutical Uses of Surfactants

    • Emulsification: Stabilize emulsions, allowing for the formulation of more stable liquid dosage forms.
    • Wetting: Improve wetting of powders for better dispersion.
    • Solubility enhancement: Increase the solubility of poorly soluble drugs.
    • Foaming agents: Form foamy products, such as mouthwashes and shampoos.
    • Detergency: Used in detergents.
    • Bioavailability enhancement: Increase the absorption of drugs from the gastrointestinal tract.

    Calculating Required HLB

    • HLB (hydrophile-lipophile balance) is a numerical value that indicates the relative strength of the hydrophilic and lipophilic portions of a surfactant molecule.
    • HLB value for an emulsion is calculated based on the HLB values of its components.
      • For an oil-in-water (O/W) emulsion, a higher HLB value (generally above 9) is required.
      • For a water-in-oil (W/O) emulsion, a lower HLB value (generally below 9) is required.
    • The proportion of surfactants needed to attain the desired HLB is determined by using the following equation: 
    Required HLB = (HLB1 x %1) + (HLB2 x %2)......

    Emulsion Preparation Methods

    Wet Gum Method

    • Procedure: Gum is dispersed in water and then oil is slowly added while stirring.
    • Used for: O/W emulsions with high viscosity.
    • Best for: Stable emulsions.

    Dry Gum Method

    • Procedure: Gum is mixed with oil, and then water is slowly added while stirring.
    • Used for: O/W emulsions.
    • Best for: Fast preparation, but may require more stirring.

    Forbes/Bottle Method

    • Procedure: Oil and water are placed in a bottle, and then a solution of the emulsifying agent is added. The bottle is shaken vigorously.
    • Used for: Forming O/W emulsions.
    • Best for: Quick formation of relatively stable emulsions.

    Beaker Method

    • Procedure: Oil and water are separately heated to a specific temperature, then slowly combined while stirring continuously.
    • Used for: O/W emulsions.
    • Best for: Controlled heating and cooling allows for stable emulsion formation.

    Forbes Method and Types of Oils

    • Suitable oils: Mineral oil and castor oil can be emulsified by this method.
    • Unsuitable oils: Oils with high viscosity and those that tend to form stable W/O emulsions (e.g., olive oil, cottonseed oil) are not suitable for this method.

    Calcium Soap Emulsions (C.S.E) vs. Soft Soap Emulsions (S.S.E)

    • C.S.E.:
      • Ingredients: Vegetable oil, lime water (calcium hydroxide solution).
      • Emulsifying agent: Calcium soaps form in situ by the reaction between the oil and lime water.
      • Emulsion type: W/O.
      • Preparation method: Either wet gum or dry gum methods can be used.
    • S.S.E.:
      • Ingredients: Vegetable oil, potassium hydroxide, water.
      • Emulsifying agent: Potassium soaps form in situ.
      • Emulsion type: O/W.
      • Preparation method: Either wet gum, dry gum, or Forbes/bottle methods can be used.

    Emulsion Instability

    • Types:
      • Creaming: The dispersed phase rises to the top or settles to the bottom of the emulsion. This is reversible.
      • Sedimentation: The dispersed phase settles to the bottom of the emulsion (more common with water-in-oil emulsions). This is reversible.
      • Coalescence: The dispersed phase droplets merge together, eventually forming a single phase. This is irreversible.
      • Phase inversion: The emulsion changes from one type to another (e.g., from an O/W to W/O emulsion). This is irreversible.

    Features of a Good Suspension

    • Uniform distribution: Particles are evenly dispersed throughout the liquid medium.
    • Good settling rate: Particles settle slowly and can be easily redispersed.
    • Physical stability: The suspension remains stable over time, preventing aggregation and clumping.
    • Good flowability: The suspension can be easily poured or dispensed.
    • Pleasing appearance: The suspension has a visually appealing appearance.
    • Taste and odor acceptable: The suspension has a taste and odor acceptable to the patient.

    Sedimentation Velocity

    • Stokes' Law governs the sedimentation velocity of particles:
    v = (2/9) * (ρp - ρl) * g * r² / η

    Where:

    • v: Sedimentation velocity

    • ρp: Density of the particle

    • ρl: Density of the liquid

    • g: Acceleration due to gravity

    • r: Radius of the particle

    • η: Viscosity of the liquid

    • Factors influencing sedimentation:

      • Particle size: Smaller particles sediment more slowly.
      • Density difference between the particle and the liquid: A smaller density difference results in slower sedimentation.
      • Viscosity of the liquid: Higher viscosity fluids lead to slower sedimentation.

    Flocculation & Deflocculation

    • Flocculation: Particles are loosely aggregated, forming a light, fluffy mass that settles quickly.
    • Deflocculation: Particles are dispersed individually and settle slowly, resulting in a dense sediment.

    Structured Vehicle & Slow Sedimentation

    • Structured vehicles: These are liquids with a high viscosity that can help slow the sedimentation of particles.
    • Mechanism: The viscous medium provides resistance to particle movement, reducing the rate of sedimentation.

    Controlled Flocculation & Suspension Properties

    • Controlled flocculation: This technique produces a suspension in which particles are loosely aggregated, forming a fluffy, easily redispersed sediment.
    • Benefits:
      • Reduced sedimentation rate.
      • Improved redispersibility.
      • Improved appearance and flowability.
    • Materials used for controlled flocculation:
      • Electrolytes: These neutralize the surface charges of particles, allowing them to flocculate.
      • Polymers: These create a network around the particles, preventing their close contact and promoting flocculation.
      • Surfactants: These can act as flocculating agents by adsorbing onto the particle surface and changing its surface charge.

    Clear and Turbid Gels

    • Clear gels: The dispersed phase is evenly distributed throughout the gel matrix, resulting in a transparent or translucent appearance.
    • Turbid gels: The dispersed phase is not uniformly distributed, resulting in a cloudy or opaque appearance.

    Gel Properties

    • Syneresis: The contraction of the gel matrix, releasing some of the liquid phase.
    • Imbibition: The ability of the gel to absorb liquid and swell in size.
    • Swelling: The increase in volume of the gel due to the absorption of liquid.

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    Description

    Test your knowledge on multi-phase systems in pharmaceuticals. This quiz covers essential concepts such as emulsions, non-Newtonian fluids, and the role of surfactants and emulsifying agents. Challenge yourself with questions about HLB values and the stability of emulsions under various conditions.

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