Suspensions in Pharmaceutical Science
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Questions and Answers

Which of the following factors does NOT influence the velocity of sedimentation in suspensions?

  • Particle size
  • Viscosity of dispersion medium
  • Density of the particles
  • Color of the particles (correct)

    • Stokes's law is applicable when particles are irregularly shaped.

    False

    What phenomenon is described as the settling of particles or floccules under gravitational force in liquid dosage forms?

    Sedimentation

    In deflocculated suspension, larger particles settle fast while smaller particles remain in the __________ liquid, making it appear cloudy.

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

    Match the following terms with their definitions:

    <p>Deflocculated suspension = Larger particles settle fast; smaller particles remain suspended Flocculated suspension = Particles form loose aggregates that settle slowly Brownian motion = Random movement of particles suspended in a fluid Stokes' Law = Equation that describes the velocity of sedimentation for spherical particles</p> Signup and view all the answers

    What occurs when particles in a suspension interfere with one another during sedimentation?

    <p>Hindered settling</p> Signup and view all the answers

    The velocity of fall of a suspended particle is greater for __________ particles than for smaller particles.

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

    What does the variable F represent in the sedimentation volume equation?

    <p>Sedimentation volume</p> Signup and view all the answers

    The minimum value of the degree of flocculation (β) is 0.

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

    What equipment is used to study the viscosity of suspensions in the rheological method?

    <p>Brookfield viscometer</p> Signup and view all the answers

    The electrokinetic method determines the __________ of the formulated suspensions.

    <p>zeta potential</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Zeta potential = Measure of particle stability in suspension Brookfield viscometer = Tool for measuring viscosity Thixotropy = Property of materials to become less viscous under shear stress Flocculated suspension = Suspension with aggregated particles</p> Signup and view all the answers

    What factors influence Van der Waals forces?

    <p>Chemical nature and particle size</p> Signup and view all the answers

    Zeta potential is related to the degree of attraction between charged particles.

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

    What is the term used to describe the difference in electric potential at the surface of a particle and the electroneutral region?

    <p>Nernst potential</p> Signup and view all the answers

    The two layers of ions at the interface constituted by charged particles are known as the _____.

    <p>electric double layer</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Nernst potential = Difference in electric potential at the surface and electroneutral region Zeta potential = Difference between shear plane and electroneutral region Deflocculation = Occurs when repulsive forces exceed attractive forces Flocculation = Aggregation of particles due to attractive forces</p> Signup and view all the answers

    When does deflocculation occur?

    <p>When zeta potential is higher than the critical value</p> Signup and view all the answers

    Adding a small amount of electrolyte can increase the zeta potential.

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

    What are counter ions also known as?

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

    The ____ of the particle is determined by potential determining ions.

    <p>electric potential</p> Signup and view all the answers

    What property do structured vehicles typically exhibit?

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

    Hydrophobic materials are easily wetted by water.

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

    What is the typical concentration of wetting agents used in formulations?

    <p>Less than 0.5%</p> Signup and view all the answers

    Surfactants reduce the _______ tension between drug particles and liquid.

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

    Match the type of wetting agent with its characteristic:

    <p>Surfactants = Decrease interfacial tension Hydrophilic colloids = Enhance stability of dispersions Solvents = Dissolve solutes Ionic surfactants = Can change the pH</p> Signup and view all the answers

    Which of the following is a common example of a wetting agent?

    <p>Sodium lauryl sulfate</p> Signup and view all the answers

    Non-ionic surfactants are generally preferred for wetting applications.

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

    Why is polysorbate 80 widely used as a wetting agent?

    <p>It is non-ionic, non-toxic, and does not change the pH of the medium.</p> Signup and view all the answers

    The HLB value of suitable wetting agents falls between _______ and _______.

    <p>7, 9</p> Signup and view all the answers

    What happens when the interfacial tension between the solid and liquid is reduced?

    <p>Liquid can penetrate better</p> Signup and view all the answers

    What is a commonly used surfactant for oral use?

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

    Hydrophilic colloids are typically cationic in nature.

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

    Name one disadvantage of using surfactants as wetting agents.

    <p>Excessive foaming</p> Signup and view all the answers

    The process of ensuring proper flocculation in a formulation is usually achieved by controlling particle size and adding _____ to enable crosslinking.

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

    Match the following wetting agents with their type:

    <p>Propylene glycol = Solvent Acacia = Hydrophilic colloid Sodium dioctylsulphosuccinate = Surfactant Xanthan gum = Hydrophilic colloid</p> Signup and view all the answers

    Which of the following is not a type of material used as a wetting agent?

    <p>Calcium carbonate</p> Signup and view all the answers

    Flocculating agents can help produce a deflocculated system.

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

    What type of agents do hydrophilic colloids mainly behave as?

    <p>Suspending agents</p> Signup and view all the answers

    _____, glycerin, and propylene glycol are examples of hygroscopic liquids used as wetting agents.

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

    Which of the following statement is true about polyelectrolytes?

    <p>They become ionized in an aqueous solution.</p> Signup and view all the answers

    What happens to the sedimentation velocity of a particle if its diameter is decreased?

    <p>It decreases</p> Signup and view all the answers

    Increasing the viscosity of the dispersion medium will enhance the settling rate of particles.

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

    What substances can be added to increase the density of the vehicle in a suspension?

    <p>polyethylene glycol, polyvinyl pyrrolidone, glycerin, sorbitol, and sugar</p> Signup and view all the answers

    The velocity of sedimentation is inversely proportional to the __________ of the dispersion medium.

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

    Match the following parameters with their effects on sedimentation:

    <p>Particle size = Larger size increases sedimentation velocity Density difference = Greater difference increases sedimentation velocity Viscosity = Higher viscosity decreases sedimentation velocity Additives = Enhance dispersion and stability</p> Signup and view all the answers

    Which of the following is a disadvantage of high viscosity in a suspension?

    <p>Hinders re-dispersibility</p> Signup and view all the answers

    Particles with a density less than the dispersion medium will sink rapidly.

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

    What parameter's increase can cause problems like pouring and syringibility in a suspension?

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

    What occurs when the zeta potential is reduced below the critical value?

    <p>Flocculation occurs</p> Signup and view all the answers

    Brownian movement helps prevent sedimentation in dispersed systems.

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

    What type of forces arise from the electric double layers surrounding particles?

    <p>Repulsive forces</p> Signup and view all the answers

    For efficient Brownian movement, the particle size should be below the critical radius (r) of approximately _____ to _____ µm.

    <p>2 to 5</p> Signup and view all the answers

    Match the following types of forces with their descriptions:

    <p>London–van der Waals forces = Forces of attraction between particles Electric double layer forces = Forces that repel particles Brownian motion = Random movement of particles in a medium Flocculation = Process of particles aggregating together</p> Signup and view all the answers

    Which of the following is a method for stabilizing suspensions?

    <p>Adding electrolytes to increase zeta potential</p> Signup and view all the answers

    Increasing the viscosity of the medium always leads to enhanced Brownian motion.

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

    How does the density of the dispersed phase affect Brownian movement?

    <p>It influences the extent of kinetic stability.</p> Signup and view all the answers

    What is the primary purpose of wetting agents in a suspension formulation?

    <p>To help disperse the drug particles in the vehicle</p> Signup and view all the answers

    A water-insoluble drug is typically the dispersed phase in an aqueous suspension.

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

    What should the particle size of the drug be for optimal performance in a suspension?

    <p>1–50 μm</p> Signup and view all the answers

    What is the sedimentation volume (F) equal to when the ultimate volume of sediment is smaller than the original volume of suspension?

    <p>0</p> Signup and view all the answers

    The primary vehicle used in suspension formulations is typically __________ or __________ water.

    <p>distilled, deionized</p> Signup and view all the answers

    In deflocculated systems, no clear boundary is formed between the sediment and the supernatant liquid.

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

    What is the term used to describe the ratio of the final volume of sediment to the original volume of the suspension?

    <p>Sedimentation volume</p> Signup and view all the answers

    Match the following components of suspensions with their functions:

    <p>Insoluble drug = Dispersed phase in suspension Vehicle = Medium for suspension Wetting agents = Enhance particle wetting Additives = Regulate flow and stability</p> Signup and view all the answers

    In a flocculated system, the flocs tend to fall together, resulting in a distinct boundary between the _____ and the supernatant.

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

    Which of the following is NOT a common ingredient in suspension formulations?

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

    Once the powder in a suspension is wetted, all soluble components can be blended into the mixture.

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

    Match the following terms with their definitions:

    <p>Electrolytes = Flocculating agents that help particles to aggregate Surfactants = Agents that reduce surface tension in liquids Flocs = Particle aggregates formed during flocculation Brownian motion = Random movement of particles suspended in a fluid</p> Signup and view all the answers

    What happens when the ultimate volume of sediment in a flocculated suspension equals the original volume of suspension?

    <p>F = 1</p> Signup and view all the answers

    What is the purpose of using flocculating agents in suspension formulations?

    <p>To improve stability and prevent sedimentation.</p> Signup and view all the answers

    Larger particles in a deflocculated suspension settle slower than smaller particles.

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

    Name one method for the formulation of suspensions.

    <p>Controlled flocculation, structured vehicle, or combination of both</p> Signup and view all the answers

    Which of the following is a function of wetting agents?

    <p>Enhance the wetting of hydrophobic particles</p> Signup and view all the answers

    The concentration of wetting agents used in formulations is typically greater than 0.5%.

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

    What is the HLB range appropriate for wetting agents?

    <p>7 to 9</p> Signup and view all the answers

    Surfactants reduce the interfacial tension between drug particles and ________.

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

    Match the following wetting agents with their characteristics:

    <p>Sodium lauryl sulfate = Anionic surfactant commonly used in cosmetics Polysorbate 80 = Non-ionic surfactant widely used in pharmaceuticals Hydrophilic colloids = Typically cationic materials Solvents = Used to dissolve solutes and enhance wetting</p> Signup and view all the answers

    What is a primary characteristic of hydrophilic materials?

    <p>Wetted easily by water</p> Signup and view all the answers

    Surfactants must always be ionic to effectively function as wetting agents.

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

    Name one disadvantage of using surfactants as wetting agents.

    <p>Potential toxicity</p> Signup and view all the answers

    Which of the following surfactants is commonly used for oral applications?

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

    Hydrophilic colloids typically behave as cationic substances.

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

    Name one disadvantage of using surfactants as wetting agents.

    <p>Excessive foaming</p> Signup and view all the answers

    Alcohol, glycerin, and propylene glycol are examples of _____ used as wetting agents.

    <p>hygroscopic liquids</p> Signup and view all the answers

    Match the following materials with their primary function:

    <p>Polysorbates = Oral surfactant Xanthan gum = Protective colloid Alcohol = Wetting agent Chitosan = Cationic hydrophilic colloid</p> Signup and view all the answers

    What is primarily achieved by using flocculating agents in formulations?

    <p>Ensure proper flocculation</p> Signup and view all the answers

    Hydrophilic materials are incompatible with quaternary ammonium compounds.

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

    What effect do hydrophilic colloids have on the viscosity of water?

    <p>They increase viscosity.</p> Signup and view all the answers

    What is zeta potential primarily related to in a suspension?

    <p>The degree of attraction between charged particles</p> Signup and view all the answers

    Flocculated suspensions exhibit dilatant flow at low shearing stress.

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

    What effect does a reduction in zeta potential below a certain value have on particle interactions?

    <p>The attractive forces exceed the repulsive forces, causing particles to aggregate.</p> Signup and view all the answers

    A well-formulated thixotropic suspension is ________ during storage but becomes fluid upon shaking.

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

    Match the type of suspension to its description:

    <p>Flocculated = Exhibits plastic or pseudoplastic flow Deflocculated = Exhibits dilatant flow Thixotropic = Loses consistency upon shaking Dilute = Exhibits low viscosity at low stress</p> Signup and view all the answers

    What method can be used to study changes in particle size in suspensions?

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

    Higher concentrations in deflocculated suspensions lead to decreased viscosity with increased shearing stress.

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

    What does the rheological behavior of flocculated suspensions depend on?

    <p>Concentration of the suspension.</p> Signup and view all the answers

    What is the primary goal of packaging suspensions?

    <p>To permit thorough mixing by shaking</p> Signup and view all the answers

    Nanosuspension particles usually have a size greater than one micron.

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

    What should be done to suspensions before each use?

    <p>They should be shaken.</p> Signup and view all the answers

    Suspensions for __________ use are formulated to control the rate of absorption of the drug.

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

    Match the following types of suspensions with their intended use:

    <p>Calamine Lotion = Topical administration Zinc Cream = Topical administration Sustained release suspensions = Controlled drug release Nanosuspensions = Oral and parenteral use</p> Signup and view all the answers

    What is NOT a recent advance in suspensions?

    <p>Flavor-enhancing suspensions</p> Signup and view all the answers

    A higher viscosity in a suspension can enhance the settling rate of particles.

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

    The average particle size of solid particles in nanosuspensions ranges between __________ and __________ nm.

    <p>200, 600</p> Signup and view all the answers

    What is the term used to describe the difference in electric potential between the surface of the particle and the electroneutral region?

    <p>Nernst potential</p> Signup and view all the answers

    Deflocculation occurs when attractive forces exceed repulsive forces.

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

    What are potential determining ions?

    <p>Anions that adsorb to the surface and give it charge</p> Signup and view all the answers

    Zeta potential is defined as the difference between the surface of the tightly bound layer and the __________ region of the solution.

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

    Match the following terms with their definitions:

    <p>Nernst Potential = Difference in electric potential at the particle surface Zeta Potential = Difference between shear plane and electroneutral region Deflocculation = Higher zeta potential than critical value Flocculation = Lower zeta potential promotes particle agglomeration</p> Signup and view all the answers

    What effect does adding a small amount of electrolyte have on zeta potential?

    <p>Decreases zeta potential</p> Signup and view all the answers

    Cations are known as potential determining ions.

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

    What governs the degree of repulsion between similarly charged particles?

    <p>Zeta potential</p> Signup and view all the answers

    What is one of the primary functions of electrolytes in flocculation?

    <p>To reduce the electric barrier between particles</p> Signup and view all the answers

    Surfactants can only be used as wetting agents and not as flocculating agents.

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

    What happens to the zeta potential of bismuth subnitrate particles when negatively charged electrolytes are added continuously?

    <p>The zeta potential changes to negative and forms a cake.</p> Signup and view all the answers

    Structured vehicles are aqueous solutions of natural and synthetic ________.

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

    What type of agents do long-chained polymers primarily act as in flocculation?

    <p>Bridging agents</p> Signup and view all the answers

    Match the following flocculating agents with their characteristic:

    <p>Electrolytes = Reduce zeta potential Surfactants = Act as wetting and flocculating agents Polymers = Form bridges between particles Structured vehicles = Increase viscosity of the suspension</p> Signup and view all the answers

    Higher viscosity in a suspension always enhances drug absorption.

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

    Too high viscosity can cause difficulties in ________ and ________.

    <p>pouring, administration</p> Signup and view all the answers

    What is the primary role of wetting agents in a formulation?

    <p>To facilitate the penetration of liquid into solid particles</p> Signup and view all the answers

    Hydrophobic materials can be easily wetted by water.

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

    What is the typical concentration of wetting agents used in formulations?

    <p>Less than 0.5 %</p> Signup and view all the answers

    Polysorbate 80 is a commonly used wetting agent due to its _______ nature.

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

    Match the following surfactants with their characteristics:

    <p>Sodium Lauryl Sulfate = Anionic surfactant Polysorbate 80 = Non-ionic surfactant Cetyl Alcohol = Emulsifying agent Tween 20 = Non-ionic surfactant</p> Signup and view all the answers

    Which of the following statements is true regarding thixotropy?

    <p>It is a characteristic of structured vehicles.</p> Signup and view all the answers

    Surfactants with an HLB value between 7 and 9 are considered unsuitable as wetting agents.

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

    What effect do surfactants have on interfacial tension?

    <p>They decrease the interfacial tension.</p> Signup and view all the answers

    What does the degree of flocculation (β) indicate?

    <p>The ratio of sedimentation volumes of flocculated and deflocculated suspensions</p> Signup and view all the answers

    The minimum value of β is 0 when the sedimentation volumes are equal.

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

    What instrument is used in the rheological method to measure the viscosity of suspensions?

    <p>Brookfield viscometer</p> Signup and view all the answers

    In the electrokinetic method, the __________ potential of formulated suspensions is measured.

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

    Match the following methods with their descriptions:

    <p>Rheological Method = Evaluates settling behavior and viscosity Electrokinetic Method = Determines zeta potential Thixotropic Evaluation = Compares flow curves of suspensions Viscometers = Instruments to measure viscosity in suspensions</p> Signup and view all the answers

    What is the role of a T-bar spindle in the Brookfield viscometer?

    <p>To descend into the suspension and measure resistance</p> Signup and view all the answers

    Cup and Bob viscometers are suitable for analyzing flocculated suspensions.

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

    What parameter does the rheological evaluation serve as a quality control measure for?

    <p>Consistency of suspensions</p> Signup and view all the answers

    Study Notes

    Suspensions

    • Dispersed systems consist of particulate matter (dispersed phase) distributed throughout a continuous medium.
    • Dispersed material ranges in size from atomic/molecular dimensions to millimeters.
    • "Disperse System" describes a system where one substance (dispersed phase) is distributed in discrete units throughout a second substance (dispersed medium).
    • Pharmaceutical suspensions are coarse dispersions (heterogeneous systems) where the internal phase (active ingredient) is evenly dispersed throughout the external phase.
    • Suspensions contain insoluble solid particles (0.5-5 microns) dispersed with a suspending agent.
    • The external phase (suspending medium) is usually aqueous, but can be organic/oily for non-oral use.
    • Finer particles may self-suspend if Brownian motion energy exceeds gravitational force, leading to low viscosity.
    • Suspensions are used as drug products and in-process materials.

    Types of Suspensions

    • Colloidal Dispersion: Particle size <1 nm, visible with electron microscope; diffuse slowly (e.g., colloidal silver, cheese, milk).
    • Coarse Dispersion: Particle size 0.1-0.2 µm or >0.2 µm, visible with microscope; do not diffuse (e.g., sand, pharmaceutical emulsions, red blood cells).
    • Nano suspensions: Biphasic colloidal dispersions of nanosized drug particles stabilized by surfactants; particle diameter typically 10-50 nanometers.

    Classification of Suspensions

    • Administration:
      • Oral (e.g., paracetamol, antacid).
      • Topical (e.g., calamine lotion).
      • Ophthalmic (e.g., prednisolone).
      • Otic (e.g., hydrocortisone-neomycin-polymyxin).
      • Rectal (e.g., barium sulfate).
      • Aerosols (e.g., tolnaftate).
      • Parenteral (e.g., vaccines, insulin zinc).
    • Physical State: Suspensions, Aerosols, Gels, Foams
    • Proportion of solid particles: Dilute (2-10% w/v solid), Concentrated (50% w/v solid).
    • Electro-kinetic nature of solid particles: Flocculated, Deflocculated

    Advantages and Disadvantages of Suspensions

    • Advantages*
    • Improved chemical stability of certain drugs (e.g., procaine penicillin G).
    • Higher bioavailability compared to other dosage forms (solution > suspension > capsule > compressed tablet > coated tablet).
    • Controlled duration and onset of action (e.g., protamine zinc-insulin suspension).
    • Masking of unpleasant/bitter taste (e.g., chloramphenicol).
    • Disadvantages*
    • Physical stability problems (sedimentation, compaction).
    • Bulky nature requiring careful handling and transport.
    • Formulation difficulty.
    • Inaccurate dosage unless packed in unit form.

    Qualities of a Good Suspension

    • Uniform content.
    • Low settling volume.
    • Absence of API crystal growth.
    • Palatability.
    • Resuspendability.
    • Absence of caking.
    • Deliverability.
    • Flow.
    • Lack of microbial growth.
    • Physical integrity.
    • Physical stability.
    • Particle adhesion to the package.
    • Polymorphic integrity.
    • Chemical stability.
    • Drug release.

    Desired Features in a Pharmaceutical Suspension

    • Particles settle slowly and are readily redispersed.
    • Viscosity allows easy pouring.
    • Chemically and physically stable.
    • Palatable (if oral).
    • Free from gritting particles.
    • Consistent particle size.

    Reasons for Formulating a Pharmaceutical Suspension

    • When the drug is insoluble in the delivery vehicle, e.g., prednisolone suspension.
    • To mask the bitter taste of the drug, e.g., chloramphenicol palmitate suspension.
    • To increase drug stability, e.g., oxytetracycline suspension.
    • To achieve controlled/sustained drug release, e.g., penicillin procaine.

    Dry Powders for Oral Suspension

    • Commercial preparations consist of dry powder mixtures or granules to be suspended in water, or another oral vehicle.
    • Most prepared products used for oral suspensions are antibiotics.
    • These products contain the antibiotic drug, colorants, flavorings, sweeteners, stabilizing agents, suspending agents, and preservatives.

    Flocculated and Deflocculated Systems

    • Flocculated Suspension:

      • Weak particle bonds form flocs.
      • Rapid settling and easy re-dispersion.
      • Less prone to compaction.
      • Flocculated particles form agglomerations that resist complete settling.

    • Deflocculated Suspension:

      • Strong particle bonds form a hard cake.
      • Slow settling and difficult re-dispersion.
      • Prone to compaction.

    Theoretical Considerations for Suspensions

    • Settling in suspensions is important to physical stability.
    • Factors influencing sedimentation velocity include:
      • Theory of Sedimentation.
      • Particle size.
      • Brownian movement.
      • Interfacial properties.
      • Electrokinetic properties.
      • Sedimentation of flocculated particles.
      • Sedimentation parameters.

    Theory of Sedimentation

    • Sedimentation is particle or floc settling under gravity in liquid.
    • Brownian motion counteracts this settling.
    • Related to particle size, density, and dispersion medium viscosity.
    • Stokes Equation describes sedimentation velocity.

    Stoke Law

    • Not applicable to irregular particles or those with hindered settling, or high concentration.
    • Sedimentation velocity is proportional to d2 (density difference).

    Particle Size

    • Critical for suspension stability.
    • Reduced particle size enhances re-dispersibility and prevents caking.
    • Symmetrical particles tend to be stable.
    • Asymmetrical particles form hard cakes.

    Density of the Vehicle

    • Increasing vehicle density can reduce sedimentation velocity.
    • Adding substances (polyethylene glycol, polyvinyl pyrrolidone, glycerin, sorbitol, sugar) to the vehicle increase its density.
    • If the density of the dispersed phase and dispersion medium are equal, the rate of settling is zero.

    Viscosity of Dispersion Medium

    • High viscosity reduces settling due to increased particles' suspending time.
    • Lower viscosity may pose problems with pouring, syringeability and re-dispersibility.

    Viscosity of Suspensions

    • Viscosity plays a key role in suspension stability and pourability.
    • Increasing viscosity decreases settling rate, hence increasing stability.

    Interfacial Properties of Suspended Particles

    • The large surface area of solid particles results in high surface free energy thus instability.
    • Flocculation (formation of flocs, light and fluffy, aggregates) occurs to reduce surface energy.
    • Wetting of particles by a vehicle is crucial to disperse the solid particles.

    Wetting of Particles

    • Wetting agents decrease interfacial tension, allowing vehicle penetration into pores.
    • Alcohol, glycerin, propylene glycol are common agents for aqueous vehicles. Mineral oil is used for non-aqueous vehicles.
    • Hydrophobic particles require more effort to wet.

    DLVO Theory

    • Describes the stability of colloidal systems based on attractive and repulsive forces between particles.

    Electrical Properties of Interfaces

    • Particles often have surface charges, so surrounding ions (cations) are attracted to create the electric double layer.
    • The adsorbed ions (anions) determine the surface potential.
    • Adhesion / clumping of these particles is minimized with an electric double layer.

    Electro-thermodynamic (Nernst) Potential

    • The difference in electric potential between a particle's surface and the electroneutral region.
    • Controlled by the electrical potential determined by the ions on the particle's surface.

    Electrokinetic or Zeta Potential

    • Potential difference between the tightly bound layer (shear plane) and the electroneutral region of the solution.
    • Governs the degree of repulsion between similarly charged particles.
    • A high zeta potential reduces attraction forces, preventing aggregation and enhancing stability.

    Deflocculation and Flocculation

    • Deflocculation: Higher zeta potential; strong repulsive forces; particles dispersed.
    • Flocculation: Lower zeta potential; attractive forces surpass repulsive forces; particles form aggregates.

    Potential Energy Curves

    • Shows attractive and repulsive forces, and net energy, as a function of the distance of separation between particles for better understanding of flocculation or deflocculation phenomena.

    Kinetic Stability of Dispersed Systems

    • Brownian movement counteracts sedimentation by keeping particles in random motion.
    • Brownian motion depends on particle size, density of dispersed phase and dispersion medium viscosity.
    • Particle size below a critical radius is key.

    Effect of Brownian Movement

    • Brownian motion counteracts particle settling.
    • Significant for small particles, but the effect is reduced in concentrated suspensions (large volume).

    Methods for Stabilizing Suspension

    • Controlling particle charges (like charges repel, preventing agglomeration), and using a solvent sheath around the particle to prevent coming close.

    Sedimentation in Different Systems

    • Flocculated systems: Particles tend to fall together, with a clear boundary between sediment and supernatant liquid.
    • Deflocculated systems: Larger particles settle faster, without a clear boundary, depending on Stokes' law.

    Sedimentation Parameters

    • Sedimentation volume (F): ratio of final sediment volume (Vu) to the initial suspension (Vo) volume.
    • F < 1 implies less sediment volume.
    • F > 1 indicates fluffy aggregates.

    The Sedimentation Behavior of Flocculated and Deflocculated Suspensions

    • Diagrams show the different settling behavior of flocculated and deflocculated suspensions.

    Methods for Formulation of Suspensions

    • Controlled flocculation using electrolytes, surfactants, polymers
    • Structured vehicles to increase viscosity
    • Combining both methods

    Addition of Electrolytes

    • Electrolytes reduce repulsive surface charges, leading to flocculation.
    • The flocculating power is strongly dependant on the valency of the ions.

    Addition of Surfactants

    • Surfactants reduce the interfacial tension between solid and liquid phases leading to enhanced wetting; can also control flocculation by changing the surface charge.

    Addition of Polymers

    • Polymers adsorb onto particles, forming a gel-like network and increasing viscosity and suspension stability through bridge formation .

    Use of Structured Vehicles

    • Aqueous solutions of natural or synthetic gums to increase viscosity and inhibit settling.
    • This is especially useful for topical suspensions.

    General Procedure for Suspension Formulation

    • Reduce particle size of insoluble drug - Levigate/grind to a smooth paste in a vehicle containing a wetting agent. - Dissolve all soluble ingredients in a portion of the vehicle and add. - Gradually add more portion of vehicle to obtain a finished suspension.

    Formulation of Suspension

    • Some dispersed phases have high affinity with the vehicle, thus readily wetted. - Other drugs or particles require initial wetting before suspension, to prevent clumping or floating. - Liquids may be mixed in phases before or after wettability.

    Flow Chart for Formulation of Suspension

    • A step-by-step process demonstrating the steps in formulating and creating a suspension

    Ingredients of Suspensions

    • Insoluble drug.
    • Vehicle (suspending medium).
    • Wetting agents.
    • Compounds that control stability and sedimentation (flocculating/suspending agents).
    • Additives for flow (e.g. viscosity modifiers). Other additives (e.g. flavour, color, sweeteners, preservatives).

    Formulation Components

    • Drug: Should be uniform particle size (1-50µm), water insoluble, surface charge characteristics must be considered.
    • Vehicle: Mostly distilled water, deionized water, alcohol, glycerol solution, non-aqueous vehicles (for topical use), structured vehicles (pseudoplastic or plastic).
    • Wetting Agents: Surfaces must be easily wetted by the vehicle, can include surfactants, hydrophilic colloids, certain solvents.

    Wetting Agents

    • Hydrophilic materials are wetted by water; hydrophobic materials require non-polar liquids.
    • Wetting agents (surfactants) are used to reduce interfacial tension between particles and liquid to facilitate wetting.
    • Examples: sodium lauryl sulfate, polysorbate 80.

    Hydrophilic Colloids

    • Examples: acacia, bentonite, tragacanth, alginates, xanthan gum.
    • Coat hydrophobic particles which imparts a hydrophilic character, improves wetting, and increases viscosity of water.
    • Act as protecting colloids, increasing stability.

    Solvents

    • Materials like alcohol, glycerol, glycols, are miscible with water to reduce interfacial tension, permitting penetration into the pores of the particles and enabling wetting.
    • Common used in conjunction with aqueous vehicles and for hydrophobic particles.

    Flocculating Agents

    • Electrolytes, surfactants, polymers.
    • Electrolytes reduce particle repulsion and induce aggregation.
    • Surfactants affect surface charges and induce aggregation.
    • Polymers bind particles to form aggregated flocs, leading to rapid settling.

    Flocculating Agents

    • Suspended particles with high charge density tend to deflocculate then cake.
    • Neutralizing the charged particles results in flocculation (aggregation in loose clusters).
    • Flocculated aggregates settle rapidly but are easily redispersed.

    Zeta Potential

    • Zeta potential is a function of a particle’s surface charge.
    • High zeta potential = increased repulsion between particles, better stability.
    • Low zeta potential = increased attraction between particles, leading to instability.

    Flocculating Agents

    • Electrolytes
    • Surfactants
    • Polymers
    • pH adjustment

    Viscosity Modifiers (Suspending Agents)

    • Typically hydrophilic polymers used to increase viscosity and retard sedimentation.
    • Hydrophilic regions interact with suspension particle surface and gel-like network is created.

    Suspending Agents

    • Polysaccharides (e.g., acacia, tragacanth, alginates, and xanthan gum).
    • Water-soluble celluloses (e.g., methylcellulose and hydroxypropylcellulose).
    • Hydrated silicates (e.g., bentonite).
    • Carbomers (e.g., carboxymethylcellulose).
    • Colloidal silicon dioxide (Aerosil).

    Other Additives

    • Buffers: Materials that resist pH change (e.g., carbonates, citrates, gluconates, phosphates). Ideal range 7.4-8.4 for suspensions
    • Preservatives: Prevent microbial growth (e.g., propylene glycol, disodium EDTA, benzalkonium chloride).
    • Sweeteners/Flavors/Colorants: Enhance palatability and appearance.

    Preparation of Suspensions

    • Precipitation Method: Insoluble drugs are dissolved in a water-miscible organic solvent, which then gets precipitated when added to water.
    • Dispersion Method: Solid particle dispersion (often using particle reduction methods) into the vehicle (which may incorporate a wetting agent).

    Evaluation of Suspensions

    • Sedimentation Method: Measures sedimentation volume (F) and degree of flocculation (β) to determine stability.
    • Rheological Method: Evaluates viscosity changes in response to shearing forces for thixotropic properties.
    • Electrokinetic Method: Measures zeta potential to assess particle stability.
    • Micromeritic Method: Measures particle size changes to determine stability.

    Rheology of Suspensions

    • Flocculated: Plastic or pseudoplastic flow, dependent on concentration.
    • Deflocculated: Dilatant flow; apparent viscosity increases with shearing stress.

    Thixotropic Properties of Suspensions

    • Thixotropic suspensions are viscous when stored but become fluid when shaken. They are beneficial to topical and certain oral medications, as well as certain parenteral injections.

    Packaging and Storage of Suspensions

    • Wide-mouth containers with adequate headspace to allow thorough mixing; tightly sealed to protect from light heat and freezing.

    Other Suspensions

    • Topical: Often semisolid, high concentrations of dispersed powder in a paraffin base; examples include lotions and pastes.
    • Parenteral: Formulated to control drug absorption rate based on size of dispensed particles; examples include, but are not limited to, eye drops, ear drops, and even some injections.

    Innovations in Suspensions

    • Nano suspensions: very fine, solid drug particles suspended for oral, topical, or parenteral administrations.
    • Taste-masked suspensions: Uses various ingredients that cover up the bitter taste, increasing patient palatability.
    • Sustained release suspensions: Coating with polymers that slow the absorption rate of the drug.

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    PHM 3110 - Lecture 9 (Coarse Dispersions - Suspensions) Lecture Notes PDF

    Description

    This quiz covers the essentials of suspensions, specifically focusing on dispersed systems in pharmaceutical applications. You'll explore the characteristics, types, and significance of suspensions in drug formulation. Test your understanding of how these systems are utilized in medicinal products and their operational contexts.

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