Pharmaceutical Emulsions Overview
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Questions and Answers

What is the HLB value of Span 80?

  • 15
  • 10.5
  • 4.3 (correct)
  • 6.2

The total percentage of emulgent blend in the formulation is 10%.

False (B)

What is the required weight of Tween 80 in the formulation?

2.9 g

The oil-soluble Span is dissolved in the oil and heated to ______°C.

<p>75</p> Signup and view all the answers

Match the following emulsifiers with their HLB values:

<p>Span 80 = 4.3 Tween 80 = 15 Liquid petrolatum = 10.5 Hydrophilic blend = 58</p> Signup and view all the answers

Which of the following compounds is used as an auxiliary emulsifying agent?

<p>Agar (C)</p> Signup and view all the answers

Finely divided solids can create emulsions that are more prone to microbial contamination.

<p>False (B)</p> Signup and view all the answers

What type of emulsion is formed if the particles are preferentially wetted by water?

<p>o/w emulsion</p> Signup and view all the answers

Compounds such as __________ and gelatin are examples of multimolecular film-forming agents.

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

Match the following emulsifying agents with their type:

<p>Potassium laurate = Monomolecular films Acacia = Multimolecular films Bentonite = Finely divided solids Agar = Auxiliary emulsifying agents</p> Signup and view all the answers

What is the main role of monomolecular films in emulsions?

<p>To lower interfacial tension and prevent coalescence (B)</p> Signup and view all the answers

Auxiliary emulsifying agents can form stable emulsions on their own.

<p>False (B)</p> Signup and view all the answers

Name one example of a finely divided solid used to stabilize emulsions.

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

What is the primary function of hydrophilic polymers in emulsion formulations?

<p>To form a multimolecular layer around oil droplets (A)</p> Signup and view all the answers

Microbial growth in emulsions primarily occurs in the oil phase.

<p>False (B)</p> Signup and view all the answers

Name one factor that complicates the preservation of o/w emulsions.

<p>The presence of a dispersed-oil phase.</p> Signup and view all the answers

The most widely used preservatives in emulsions are a mixture of __________ and __________.

<p>Methyl parahydroxybenzoate, Propyl parahydroxybenzoate</p> Signup and view all the answers

What role do hydrocolloids play in emulsions?

<p>They act as a coating around the droplets. (C)</p> Signup and view all the answers

Emulsifiers with an HLB value between 3-6 are preferred for o/w emulsions.

<p>False (B)</p> Signup and view all the answers

At what pH is Benzoic acid effective as a preservative?

<p>Below 5 (A)</p> Signup and view all the answers

What is one example of an ingredient that can support microbial growth in emulsions?

<p>Arachis oil</p> Signup and view all the answers

Name one example of a solid particle that forms stable films in emulsions.

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

Match the following preservatives with their effective concentrations:

<p>Methyl parahydroxybenzoate = 0.2% Benzoic acid = 0.1% Chlorocresol = 0.1% Phenoxyethanol = 1%</p> Signup and view all the answers

Particles must be wetted by both phases to remain at the ______ and form a stable film.

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

Which HLB range is associated with using emulsifiers in antifoaming agents?

<p>0-3 (D)</p> Signup and view all the answers

What is the total required HLB number for the emulsion?

<p>12.1 (B)</p> Signup and view all the answers

The un-ionized form of weak acid preservatives tends to partition into micelles and oil droplets.

<p>True (A)</p> Signup and view all the answers

Match the following HLB ranges with their applications:

<p>0-3 = Antifoaming agents 3-6 = w/o emulsifying agent 8-18 = o/w emulsifying agents 10-18 = Solubilizing agents</p> Signup and view all the answers

The proportion of liquid paraffin in the oil phase is 94.6%.

<p>True (A)</p> Signup and view all the answers

What percentage of Tween 80 is used in the formulation?

<p>3.6%</p> Signup and view all the answers

It is easier to form an o/w emulsion using lipophilic emulsifiers.

<p>False (B)</p> Signup and view all the answers

The ______ of an emulsifier relates to its hydrophilic and lipophilic tendencies.

<p>HLB (Hydrophile/Lipophile Balance)</p> Signup and view all the answers

The two hydrophilic and hydrophobic surfactants used in the formulation are __________ and __________.

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

Which of the following is not a vegetable oil used in the oil phase of pharmaceutical emulsions?

<p>Petrolatum (B)</p> Signup and view all the answers

Which surfactant has the highest HLB value?

<p>Sodium dodecyl (lauryl) Sulphate (A)</p> Signup and view all the answers

Polysorbate 60 has an HLB value of 12.9.

<p>False (B)</p> Signup and view all the answers

What is the required HLB value for beeswax in a w/o emulsion?

<p>5</p> Signup and view all the answers

The HLB value of sorbitan mono-stearate (Span 60) is ______.

<p>4.7</p> Signup and view all the answers

Match the surfactants to their HLB values:

<p>Sorbitan tri-oleate (Span 85) = 1.8 Polysorbate 80 (Tween 80) = 15.0 Oleic acid = 4.3 Sorbitan mono-laurate (Span 20) = 8.6</p> Signup and view all the answers

In an o/w emulsion, which of the following surfactants would be suitable with an HLB requirement of 12?

<p>Polysorbate 80 (Tween 80) (A)</p> Signup and view all the answers

Sorbitan mono-oleate (Span 80) has the same HLB value as oleic acid.

<p>True (A)</p> Signup and view all the answers

Which emulsifying agent should be chosen if the required HLB for an oil phase is known to be 10?

<p>One with HLB above 10 and one below 10.</p> Signup and view all the answers

Flashcards

Finely divided solids as emulsifiers

Finely divided solids can be adsorbed at the oil-water interface, preventing globule coalescence. The type of emulsion depends on the solid's affinity for oil or water.

Monomolecular Films

These agents form a single layer of molecules or ions around dispersed droplets, preventing them from merging. They lower surface tension, contributing to stability.

Multimolecular Films

They form multiple layers of molecules around dispersed droplets, creating a strong, rigid film that stabilizes the emulsion.

Auxiliary Emulsifying Agents

These agents are not capable of forming stable emulsions on their own. They act as thickeners, increasing the viscosity of the continuous phase, leading to improved emulsion stability.

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Water-in-oil emulsion (W/O)

A type of emulsion where water is dispersed as droplets within an oil continuous phase.

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Oil-in-water emulsion (O/W)

A type of emulsion where oil is dispersed as droplets within a water continuous phase.

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Thickening Agents

These agents are normally incapable of forming stable emulsions themselves, but help stabilize by increasing the consistency of the emulsion's continuous phase.

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Hydrophilic and Hydrophobic

The ability of an emulsifier to attract and hold either oil or water.

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Emulsifier Film

A coating that surrounds droplets in an emulsion, preventing them from merging, even without a strong surface charge.

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Hydrocolloid Emulsifier

A type of emulsifier that increases the viscosity of the water phase, making it harder for droplets to move and separate.

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Solid Particle Film Emulsifier

Solid particles that form a film around droplets, stabilizing the emulsion by acting as a physical barrier. Examples include bentonite, graphite, and magnesium hydroxide.

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HLB (Hydrophile-Lipophile Balance)

A system used to classify emulsifiers based on their balance between hydrophilic (water-loving) and lipophilic (oil-loving) properties.

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o/w Emulsion (Oil-in-Water)

Emulsifiers with a high HLB (8-18) are more likely to form oil-in-water (o/w) emulsions, where oil droplets are dispersed in water.

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w/o Emulsion (Water-in-Oil)

Emulsifiers with a low HLB (3-6) are more likely to form water-in-oil (w/o) emulsions, where water droplets are dispersed in oil.

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Antifoaming Agent

A surfactant that prevents foam formation, typically with an HLB range of 0-3.

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Wetting Agent

A surfactant used to make a substance more easily wetted by a liquid. Typically has an HLB range of 7-9.

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Surfactant Blend

A mixture of surfactants with different HLB values to achieve a desired HLB value for a specific application.

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HLB Calculation

The process of calculating the required percentages of each surfactant in a blend to achieve a specific HLB value.

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Emulsion Preparation (Heating Method)

A method of preparing an emulsion by heating both oil and water phases separately, then mixing them together while continuously stirring until cool.

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Emulsion Formulation (Surfactant Selection)

The process of selecting the appropriate surfactants and proportions for the blend, considering the HLB required for the specific emulsion.

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HLB Value

A number indicating a surfactant's hydrophilic-lipophilic balance, ranging from 0 (very lipophilic) to 20 (very hydrophilic).

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O/W Emulsifier

A surfactant that helps form an oil-in-water (o/w) emulsion, where tiny oil droplets are dispersed in water.

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W/O Emulsifier

A surfactant that helps form a water-in-oil (w/o) emulsion, where tiny water droplets are dispersed in oil.

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Required HLB Value

The specific HLB value needed to emulsify a particular oil effectively.

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Oil-in-Water (o/w) Emulsion

A type of emulsion where oil droplets are dispersed in a continuous water phase.

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Water-in-Oil (w/o) Emulsion

A type of emulsion where water droplets are dispersed in a continuous oil phase.

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Emulsifier Blending

A blend of two surfactants, one with a higher HLB and one with a lower HLB, to achieve the required HLB for a specific oil and emulsion type.

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Emulsification

The process of creating a stable mixture of two immiscible liquids (like oil and water) by using surfactants.

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HLB (Hydrophilic-Lipophilic Balance)

A measure of the balance between hydrophilic and hydrophobic properties of a molecule. It is used to predict the emulsifying properties of surfactants.

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Emulsifier Blend

The ratio of hydrophilic (water-loving) surfactant to hydrophobic (oil-loving) surfactant used in an emulsion. It determines the type of emulsion (oil-in-water or water-in-oil).

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Surfactant

A substance that reduces the interfacial tension between oil and water, allowing them to mix more readily.

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Emulsion

A mixture of oil and water where one phase is dispersed in the other as tiny droplets.

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Hydrophobic Proportion

The fraction of a substance that is hydrophobic, often expressed as a percentage.

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Hydrophilic Proportion

The fraction of a substance that is hydrophilic, often expressed as a percentage.

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Preservative Partitioning in Emulsions

The movement of a substance from an area of high concentration to an area of low concentration, driven by a difference in potential. This happens when the preservative molecules move from the continuous phase (water) into the dispersed oil phase.

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Preservatives for Emulsions

These are used to protect emulsions from spoiling by microbial contamination. They work by inhibiting the growth of microorganisms in the aqueous phase of the emulsion.

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Methyl Parahydroxybenzoate and Propyl Parahydroxybenzoate

This is the most widely used preservative for emulsions. It is a mixture of methyl parahydroxybenzoate and propyl parahydroxybenzoate.

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pH and Preservative Effectiveness

The pH of the emulsion can affect the effectiveness of the preservative. An optimal pH range is needed to ensure that the preservative is in its active form.

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Hydrophilic Polymers and Preservatives

Hydrophilic polymers can bind to preservatives, reducing their availability in the aqueous phase, decreasing their effectiveness.

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Oil Droplets and Preservative Availability

The presence of dispersed oil droplets can reduce the concentration of preservatives in the continuous aqueous phase, which is where they are needed to inhibit microbial growth.

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Study Notes

Coarse Dispersion, Emulsion

  • Pharmaceutical emulsions consist of two liquid phases: an aqueous phase and an oil phase.
  • The aqueous phase is often purified water for oral or topical administration, or sterile water for injections for intravenous administration.
  • Buffers (citrate or phosphate) might be added to control pH in the aqueous phase.
  • The type of emulsion (oil-in-water (o/w) or water-in-oil (w/o)) depends on the emulsifier's solubility.
  • If the emulsifier is more soluble in water, the water phase is continuous (o/w).
  • Conversely, if the emulsifier is more soluble in oil, the oil phase is continuous (w/o).
  • Adding a substance that alters the emulsifier's solubility can cause a phase inversion.

Excipients in Pharmaceutical Emulsions

  • Surface-active agents (surfactants) are a major category of excipients in pharmaceutical emulsions.
  • To enhance physical and chemical stability, and to make the formulation aesthetically pleasing to the patient, other excipients are also used.

Emulsifying Agents

  • Emulsifying agents reduce interfacial tension, maintain droplet separation, and act as a barrier at the interface.
  • Effective emulsifying agents are surface-active agents.
  • These agents have hydrophilic (water-loving) polar groups oriented towards the water and lipophilic (oil-loving) nonpolar groups oriented towards the oil.
  • Emulsion type depends on the solubility of the emulsifying agent; hydrophilic agents result in o/w emulsions, while lipophilic agents result in w/o emulsions.
  • Emulsifying agents can be categorized into naturally occurring, surfactants, and finely divided solid substances.

Naturally Occurring Emulsifying Agents

  • These agents originate from plant or animal sources.
  • Examples include:
    • Polysaccharides (Acacia, tragacanth, starch, pectin, carrageenan): Acacia is a good emulsifier for oral emulsions, while tragacanth increases viscosity
    • Semi-synthetic polysaccharides (methylcellulose and carboxymethylcellulose): Form o/w emulsions.
    • Sterol-containing substances (beeswax, wool fat, wool alcohols): Function as w/o emulsifying agents
    • Proteins (gelatin): Produce o/w emulsions
    • Phospholipids (lecithin): Major emulsifier in egg yolk; gives o/w emulsions.

Surfactants

  • Surfactants have both hydrophilic and lipophilic regions, classified as anionic, cationic, nonionic, or amphoteric.
  • Anionic surfactants (e.g., sodium stearate) are commonly used, but their compatibility with some inorganic cations is limited, and they are comparatively more toxic than other types.
  • They are commonly used in external formulations for o/w emulsions.
  • Cationic and nonionic surfactants also play a role.

Amphoteric Surfactants

  • Amphoteric surfactants have both positive and negative charges, depending on pH.
  • Lecithin is a notable example of an amphoteric surfactant and is used in o/w emulsions and creams.

Finely Divided Solids

  • Finely divided solids (e.g., bentonite, graphite, magnesium hydroxide) can adsorb at the oil-water interface, preventing droplet coalescence, and improving the stability of emulsions.

Auxiliary Emulsifying Agents

  • Auxiliary emulsifying agents aren't effective emulsifiers by themselves but function as thickening agents, increasing emulsion stability.
  • Examples include tragacanth and agar.

Mechanism of Action of Emulsifying Agents

  • Emulsifying agents form monomolecular or multimolecular films at the oil-water interface to prevent droplet coalescence.
  • Hydrophilic agents yield o/w emulsions, while hydrophobic agents create w/o emulsions.

HLB Values

  • HLB (hydrophile-lipophile balance) values guide surfactant selection for specific emulsion types (o/w or w/o).
  • An HLB value above 8-18 is typically used for o/w emulsions, while values below 8-18 are preferred for w/o emulsion types.

Formulation

  • The total required HLB is calculated based on the HLB values of individual oils or other ingredients.
  • The chosen emulsifiers' HLB values are combined to match the desired final emulsion type.

Antioxidants

  • Antioxidants are used to enhance the stability of drugs and oils (vegetable oils) against oxidation.
  • Examples of lipophilic antioxidants include butylated hydroxyanisole, butylated hydroxytoluene, and propyl gallate.
  • Water-soluble antioxidants, such as sodium metabisulphite or sodium sulphite, are used in the aqueous phase.

Flavours and Sweeteners

  • Flavors and sweeteners can be added to mask the taste of the active ingredient or the oil phase.
  • Viscosity modifiers: Used to influence emulsion stability and prevent creaming.

Preservatives

  • Preservatives are used to prevent microbial growth. Choice of preservatives depends on pH, presence of polymers, and how they are partitioned between phases (oil and water). For emulsions, preservation can be complicated by the partitioning of the preservative.

Vegetable Oils as Oil Phase

  • Vegetable oils (e.g., cottonseed, arachis, almond oils) are common oil phases in pharmaceutical emulsions.
  • They are composed of mono-, di-, and triglycerides of saturated and unsaturated fatty acids.

Non-Aqueous Oil Phases

  • Petrolatum, mineral oil, isopropyl myristate are alternative non-aqueous oil phases.

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Lecture 10: Pharmaceutical Emulsions PDF

Description

This quiz covers the fundamental concepts of pharmaceutical emulsions, including the phases involved and the role of emulsifiers. Learn about the types of emulsions and the importance of excipients in enhancing their stability and efficacy. Test your knowledge of the scientific principles behind these critical formulations.

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