Pharmaceutical Science: Coarse Dispersion Quiz
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Questions and Answers

What defines a coarse dispersion?

  • Particles that are both soluble and miscible with the dispersion medium.
  • Particles ranging from 0.1 to 0.5 μm in size.
  • Particles that are in the colloidal range of 0.5 to 10 μm.
  • Particles usually larger than 10 μm in size. (correct)

    • What is the primary characteristic of a suspension?

  • It features solid particles that are completely soluble in the liquid medium.
  • It contains solid particles typically larger than 0.1 µm dispersed in a liquid medium. (correct)
  • It relies on volatile components to maintain distribution.
  • It contains liquid droplets dispersed in a solid medium.

    • How are most dry powder suspensions prepared for administration?

  • They are mixed with a solid vehicle and compressed.
  • They are simply stored until required for immediate use.
  • They are already in solution and do not require any further preparation.
  • They are diluted and agitated with a specified quantity of vehicle. (correct)

    • What size particles are classified as fine dispersions?

    <p>Particles ranging from 0.5 to 10 μm.</p> Signup and view all the answers

    Which of the following correctly describes emulsions?

    <p>They have a liquid dispersed phase that is neither soluble nor miscible with the dispersing liquid.</p> Signup and view all the answers

    What is essential for the accurate administration of suspensions?

    <p>Agitating the container moderately to ensure uniformity.</p> Signup and view all the answers

    What is a common reason for supplying certain drugs as dry powder mixtures?

    <p>They can become unstable in aqueous vehicles over time.</p> Signup and view all the answers

    Which of the following best describes a dispersed system?

    <p>A system comprising immiscible or undissolved substances distributed throughout another phase.</p> Signup and view all the answers

    What is a consequence of increasing the viscosity of a suspension excessively?

    <p>It complicates the flow and dispersion of the suspension.</p> Signup and view all the answers

    What is the purpose of using surface-active agents as wetting agents?

    <p>To reduce interfacial tension between solid and liquid</p> Signup and view all the answers

    Which of the following suspending agents is NOT mentioned as a thickening agent?

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

    What defines a flocculated suspension?

    <p>Particles are weakly bonded and resuspend easily.</p> Signup and view all the answers

    Which of the following surfactants is commonly used as an external wetting agent?

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

    How does particle size affect the sedimentation rate of a suspension?

    <p>Larger particles settle faster than smaller particles.</p> Signup and view all the answers

    What is a disadvantage of using surface-active agents as wetting agents?

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

    What is a potential issue when using hydrophilic colloids as suspending agents?

    <p>They bind medicinal agents, reducing therapeutic effect.</p> Signup and view all the answers

    Hydrophilic colloids behave as protective colloids by doing what?

    <p>Coating solid hydrophobic particles with a multimolecular layer</p> Signup and view all the answers

    Which materials are mentioned as hydrophilic colloids that can enhance wetting?

    <p>Acacia and xanthan gum</p> Signup and view all the answers

    What happens when the particle size in a suspension is reduced too much?

    <p>They may form a compact cake upon settling.</p> Signup and view all the answers

    What role do solvents like alcohol and glycerol play in enhancing wetting?

    <p>They penetrate and displace air from powder agglomerates</p> Signup and view all the answers

    Which aspect should be carefully calibrated when adding a suspending agent?

    <p>The amount to avoid excessive viscosity.</p> Signup and view all the answers

    What is one characteristic of surfactants suitable for use as wetting agents?

    <p>An HLB value between 7 and 9</p> Signup and view all the answers

    Which of the following is true about deflocculated suspensions?

    <p>They are characterized by a hard sediment cake.</p> Signup and view all the answers

    What is a possible effect of using hydrophilic colloids at low concentrations?

    <p>Formation of a deflocculated system</p> Signup and view all the answers

    What is the primary role of acacia in pharmaceutical preparations?

    <p>It serves as a suspending agent.</p> Signup and view all the answers

    Which property makes tragacanth a better thickening agent than acacia?

    <p>It forms more viscous aqueous solutions.</p> Signup and view all the answers

    What happens to alginate mucilages if heated above 60°C?

    <p>They will lose their suspending properties.</p> Signup and view all the answers

    What is the main disadvantage of using sodium alginate in certain formulations?

    <p>It can be incompatible with cationic materials.</p> Signup and view all the answers

    How does the addition of calcium chloride affect sodium alginate?

    <p>It produces calcium alginate with higher viscosity.</p> Signup and view all the answers

    What effect does acacia mucilage's acidity have over time?

    <p>It can cause deterioration of susceptible active agents.</p> Signup and view all the answers

    Which polysaccharide is known for its thixotropic and pseudoplastic properties?

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

    Over what pH range do alginates exhibit maximum viscosity?

    <p>5-9</p> Signup and view all the answers

    What role do wetting agents play in the formulation process?

    <p>They act as dispersants in an aqueous vehicle.</p> Signup and view all the answers

    How can controlled flocculation be achieved?

    <p>Through particle size control and polymers.</p> Signup and view all the answers

    What is the function of zeta potential in colloidal systems?

    <p>It reflects the surface charge affecting stability.</p> Signup and view all the answers

    What is a key characteristic of trivalent ions compared to mono- or divalent electrolytes?

    <p>They are more efficient but more toxic.</p> Signup and view all the answers

    What happens if too much electrolyte is added to a colloidal suspension?

    <p>It may cause charge reversal and deflocculation.</p> Signup and view all the answers

    Which type of agents are added to enable crosslinking between particles during formulation?

    <p>Polymers.</p> Signup and view all the answers

    Which of the following is NOT considered a common electrolyte used in formulations?

    <p>Potassium sulfate.</p> Signup and view all the answers

    What is the primary effect of adding inorganic electrolytes to aqueous suspensions?

    <p>They alter the zeta potential of dispersed particles.</p> Signup and view all the answers

    What role do electrolytes play in flocculation?

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

    Why might non-ionic surfactants affect flocculation despite having a negligible effect on charge density?

    <p>They adsorb onto multiple particles due to their linear configurations.</p> Signup and view all the answers

    Which of the following materials does NOT act as a polymeric flocculating agent?

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

    What happens to sedimentation volume when polymeric flocculating agents are used?

    <p>It remains large for a considerable period.</p> Signup and view all the answers

    How do suspending agents affect sedimentation in a suspension?

    <p>They entrap dispersed particles within a gel-like network.</p> Signup and view all the answers

    Which of the following is a characteristic of suitable suspending agents?

    <p>They can be effective at low concentrations.</p> Signup and view all the answers

    Which of the following polysaccharides is commonly used as a suspending agent?

    <p>Xanthan gum</p> Signup and view all the answers

    What can be a consequence of using large quantities of suspending agents?

    <p>Altered degree of flocculation.</p> Signup and view all the answers

    Study Notes

    Heterogeneous System - Coarse Dispersion

    • Liquid preparations contain undissolved or immiscible drugs distributed throughout a vehicle.
    • The dispersed substance is the dispersed phase.
    • The vehicle is the dispersing phase or dispersion medium.
    • Suspensions: Solid materials are insoluble in the dispersion medium.
    • Emulsions: The dispersed phase is a liquid immiscible with the liquid dispersion phase.
    • Aerosols: The dispersed phase can be small air bubbles in a solution or emulsion.
    • Particle size of coarse dispersions: 10-50 µm.
    • These include suspensions and emulsions.
    • Particle size of fine dispersions: 0.5-10 µm (collodial range)
    • Fine dispersions include Magmas and gels.
    • Colloidal dispersions are in the colloidal range.
    • Complete and uniform redistribution of the dispersed phase is essential for accurate administration of uniform doses.
    • This is achieved through moderate agitation.

    Suspensions

    • Contain finely divided drug distributed somewhat uniformly throughout a vehicle.
    • The drug has minimal solubility in the vehicle.
    • Pharmaceutical suspension: Coarse dispersion of insoluble solid particles in a liquid medium.
    • Particle diameters are generally greater than 0.1 µm.
    • Some suspensions are available in ready-to-use form, already dispersed in a liquid vehicle, with or without stabilizers and additives.
    • Some suspensions are available as dry powders intended for suspension preparation in a liquid vehicle.
    • Often contain the drug, suitable suspending & dispersing agents for dilution and agitation in purified water.
    • Some drugs (e.g., antibiotics) are unstable in an aqueous medium and are supplied as dry powder mixtures for reconstitution.

    Reasons for Suspensions

    • Certain drugs are chemically unstable in solution but stable when suspended.
    • This ensures chemical stability for liquid therapies, particularly with infants, children and the elderly.
    • The disagreeable taste of certain drugs can be overcome when administered undissolved as an oral suspension.
    • Example: Erythromycin estolate (less water-soluble ester form of erythromycin) is used in oral suspension to increase palatability.
    • Usually aqueous preparations, flavoured, and sweetened to suit the patient.

    Features Desired in a Pharmaceutical Suspension

    • Therapeutically active, chemically/physically stable, and aesthetically appealing.
    • Remain homogenous for a period of time.
    • Settle slowly and redisperse readily upon gentle shaking.
    • Particles must not form a hard cake at the bottom.
    • Particle size should remain fairly constant throughout time.
    • Should pour readily and evenly from the container.

    Sedimentation Rate of the Particles of a Suspension

    • Stokes' Law Equation: dx/dt = d² (ρ₁ - ρ₂)/18η
    • Factors involved in settling rate:
    • 'dx/dt' is the rate of settling.
    • 'd' is the diameter of the particle.
    • 'ρ₁' is the density of the particles.
    • 'ρ₂' is the density of the medium.
    • 'g' is the gravitational constant.
    • 'η' is the viscosity of the medium.
    • Factors affecting physical stability: particle diameter, density, viscosity of the medium.
    • Greater particle density leads to faster sedimentation.
    • Aqueous vehicles commonly used, so particle density is usually greater than the vehicle density, which is desirable.

    • Viscosity of the medium may be increased to reduce sedimentation rate.

    Sedimentation in Different Systems

    • In flocculated systems, the flocs tend to settle together, with a distinct, clear boundary between the sediment and the supernatant, which is clear.
    • In deflocculated systems, sedimentation occurs more slowly, with no distinct boundary between, the sediment and supernatant, which remains turbid ("cloudy") for a longer period.

    Sedimentation Parameters

    • Sedimentation volume (F) is the ultimate volume of sediment (Vu) divided by the original volume of the suspension (Vo)
    • If Vu is smaller than Vo , F = 0.5
    • If Vu is equal to Vo , F = 1
    • It is possible for F to be greater than 1.

    Evaluation of Suspensions

    • Techniques to screen initial preparations & compare products.
    • Sedimentation volume (F).
    • Redispersability (number of inversions necessary to redisperse the sediment).
    • Rheological characteristics (flow properties).

    Suspension Components

    • Insoluble drug
    • Vehicle (suspending medium)
    • Wetting agent
    • Flocculating/suspending agent
    • Additives to control flow behavior
    • pH regulators
    • Other additives

    Wetting Agents

    • Some insoluble solids are easily wetted by water and disperse readily in the aqueous phase with little agitation.

    • Most require additional wetting agents.

    • To ensure adequate wetting, interfacial tension between the solid and the liquid must be reduced.

    • Wetting agents:
      1. Surface-active agents (e.g., polysorbates, sorbitan esters, sodium lauryl sulfate, sodium dioctylsulphosuccinate).
      2. Hydrophilic colloids (e.g., acacia, alginates, bentonite).
      3. Solvents (e.g., alcohol, glycerol, propylene glycol).

    Flocculating Agents

    • Achieved by a combination of particle size control, electrolytes to control zeta potential and polymers to enable crosslinking between particles.
    • Electrolytes: reduce the electric barrier between particles.
    • Surfactants may neutralise surface charges.
    • Polymers: form a gel-like network within the system to hold the dispersed particles in flocculated state.

    Zeta Potential

    • Zeta potential is related to electrostatic repulsion between the particles and colloidal stability.

    Flocculating Agents

    • Electrolytes

    • Surfactants

    • Polymers

    • Alteration in pH of preparation to minimum drug solubility

    Viscosity Modifiers (Suspending Agents)

    • High disperse phase concentration, sufficient viscosity in absence of flocculating agent.
    • Suspending agents used to increase apparent viscosity.
    • Suitable materials are hydrophilic polymers.
    • They entrap solid particles within their gel-like network to prevent sedimentation.

    Suspending Agents

    • 1. Polysaccharides (e.g., Acacia, Tragacanth, Alginates, Starch, Xanthan gum)
    • 2. Water-soluble Celluloses (e.g., Methylcellulose, Hydroxyethylcellulose, Carmellose sodium, Microcrystalline cellulose)
    • 3. Hydrated Silicates (e.g., Bentonite, Magnesium aluminium silicate, Hectorite)
    • 4. Carbomers (e.g., carboxypolyethylene)
    • 5. Colloidal silicon dioxide (Aerosil®)

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    Related Documents

    BSPh-203-Unit-4.2-Coarse-Dispersion PDF

    Description

    Test your understanding of heterogeneous systems in pharmaceutical preparations, focusing on coarse dispersions such as suspensions, emulsions, and aerosols. Learn about the importance of particle size, redistribution, and accurate administration in drug formulations. This quiz will challenge your knowledge of key concepts related to coarse dispersions.

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