Introduction to Suspensions and Their Properties
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Questions and Answers

What causes the yield value in flocculated suspensions?

  • Increased particle size
  • Addition of stabilizing agents
  • Higher viscosity at low shear
  • Interparticle van der Waals forces (correct)

    • Which property characterizes deflocculated suspensions?

  • High yield value
  • Low yield value
  • Constant viscosity regardless of stress
  • Viscosity increases with applied stress (correct)

    • What is the first step in the preparation of suspensions?

  • Addition of the remaining ingredients
  • Stabilization of dispersed solid
  • Wetting and dispersion of the active ingredient (correct)
  • Final mixing of all components

    • What is a common method for dispersing polymers in water?

    <p>Creating a paste in glycerin first</p> Signup and view all the answers

    Why are electrolytes added during stabilization of dispersed solids?

    <p>To produce charges for repulsion</p> Signup and view all the answers

    What material can be treated to aid in wetting drug powders?

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

    What is the effect of flocculation on the yield value of a suspension?

    <p>It raises the yield value</p> Signup and view all the answers

    Which of the following is true about dilatant behavior in suspensions?

    <p>Viscosity increases with increasing stress</p> Signup and view all the answers

    What type of suspension is formulated primarily for parenteral use?

    <p>Parenteral suspension</p> Signup and view all the answers

    Which of the following is true about colloidal suspensions?

    <p>They have solid particles smaller than 1 micron.</p> Signup and view all the answers

    What role do counter ions play in a system with potential-determining ions?

    <p>They are oppositely charged to potential-determining ions.</p> Signup and view all the answers

    Which statement best describes the effects of particle size in suspensions?

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

    What effect do electrolytes have on zeta potential in suspensions?

    <p>Decrease the zeta potential leading to flocculation.</p> Signup and view all the answers

    What is the diameter range for particles that experience notable Brownian movement?

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

    Which ingredient is essential for the formulation of a suspension to control stability and sedimentation?

    <p>Flocculating agent</p> Signup and view all the answers

    Which factor increases the flocculating power of electrolytes?

    <p>The valency of the ions used.</p> Signup and view all the answers

    What distinguishes a concentrated suspension from a dilute suspension?

    <p>The amount of solid particles exceeding 10% w/v.</p> Signup and view all the answers

    What happens to bismuth subnitrate particles when monobasic potassium phosphate is added?

    <p>The positive zeta potential decreases due to adsorption.</p> Signup and view all the answers

    What is the primary characteristic of a pharmaceutical suspension?

    <p>Contains finely divided drug particles in a liquid vehicle</p> Signup and view all the answers

    According to Stokes' law, which variable does NOT influence the velocity of settling in a suspension?

    <p>Temperature of the solution</p> Signup and view all the answers

    What effect does dividing a solid into smaller particles have on surface free energy?

    <p>Increases the free energy by increasing surface area</p> Signup and view all the answers

    Which of the following is NOT a physical property of a well-formulated suspension?

    <p>Particles should sediment on the bottom</p> Signup and view all the answers

    What is the significance of surface free energy in flocculation?

    <p>Lowering surface free energy promotes particle attraction.</p> Signup and view all the answers

    Structured vehicles in suspensions are designed primarily to do what?

    <p>Facilitate shaking without caking</p> Signup and view all the answers

    Which of the following is a characteristic of deflocculated suspensions?

    <p>Particles remain uniformly distributed longer.</p> Signup and view all the answers

    What is the primary reason for controlling the particle size in suspensions?

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

    What characteristic do surfactants used as flocculating agents possess?

    <p>They can be both ionic and non-ionic.</p> Signup and view all the answers

    What is a characteristic of thixotropic compounds in structured vehicles?

    <p>They decrease viscosity upon agitation</p> Signup and view all the answers

    What is a key advantage of using suspensions for drug delivery?

    <p>Easier to administer to patients with swallowing difficulties</p> Signup and view all the answers

    How do flocculated suspensions differ from deflocculated suspensions?

    <p>Flocculated suspensions settle faster and can be more easily re-dispersed</p> Signup and view all the answers

    What layer on the surface of solid particles makes it difficult to disperse them in a liquid vehicle?

    <p>Layer of adsorbed air</p> Signup and view all the answers

    What occurs when the zeta potential of a suspension reaches zero?

    <p>Flocculation starts to occur.</p> Signup and view all the answers

    What parameter is NOT typically considered when analyzing an insoluble drug for suspension formulation?

    <p>Color of the drug</p> Signup and view all the answers

    Which of the following is an example of a suspending medium?

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

    What range of solid particle sizes is typically found in suspensions?

    <p>0.5 to 5.0 microns</p> Signup and view all the answers

    Which of the following statements about sodium and calcium ions is true?

    <p>Calcium ions provide stronger flocculating power due to higher valency.</p> Signup and view all the answers

    What term describes powders that are not easily wetted by water?

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

    How is wettability of a powder typically determined?

    <p>By observing the contact angle and spreading coefficient</p> Signup and view all the answers

    What role do wetting agents play in the formulation of suspensions?

    <p>Reduce the surface tension of liquids</p> Signup and view all the answers

    Which of the following applications is suitable for suspensions?

    <p>To deliver insoluble or poorly soluble drugs orally</p> Signup and view all the answers

    What characteristic should settled particles in a suspension have?

    <p>Easily re-disperse when shaken</p> Signup and view all the answers

    What does a positive spreading coefficient (Sc) indicate about the wetting of a powder?

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

    What is the primary concern if deflocculated particles are used in a structured vehicle?

    <p>They could lead to the formation of solid hard cakes</p> Signup and view all the answers

    Which of the following is a widely used non-ionic surfactant that does not change the pH of the medium?

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

    Which statement is true regarding the stability of suspensions?

    <p>Suspensions should be chemically and physically stable</p> Signup and view all the answers

    What effect does a surfactant have on the interfacial tension between a solid and a liquid?

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

    What is indicated by a lower contact angle in wetting phenomena?

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

    What is the main purpose of wetting agents in solid-liquid dispersions?

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

    Study Notes

    Introduction to Suspensions

    • Suspensions are liquid preparations containing finely divided drug particles uniformly distributed in a suitable vehicle.
    • The drug in a suspension exhibits a minimum degree of solubility in the dispersion medium.
    • The size of solid particles in suspensions ranges from 0.5 to 5.0 microns.

    Properties of a Well-Formulated Suspension

    • Particles should not sediment in the container during storage.
    • Settled particles should not form a hard cake.
    • Settled particles should be easily re-dispersed by gentle shaking.
    • The suspension should remain homogeneous between shaking and dose removal.
    • The suspension should be free from gritting particles.
    • The suspension should be pleasant and palatable.
    • The suspension should be chemically and physically stable (not temperature sensitive).

    Pharmaceutical Applications of Suspensions

    • Suspensions are used as oral drug delivery systems for insoluble or poorly soluble drugs with difficulties swallowing solid dosage forms (e.g., children, elderly).
    • Suspensions can overcome drug instability in aqueous solutions.
    • Insoluble or poorly soluble drugs that degrade in water can be suspended in non-aqueous vehicles.

    Classifications of Suspensions

    • General Classes: Oral, externally applied, parenteral
    • Size of Solid Particles: Colloidal (<1 micron), Coarse (>1 micron), Nano (10 nm)
    • Proportion of Solid Particles: Dilute (2-10% w/v), Concentrated (50% w/v)
    • Electro-kinetic Nature of Solid Particles: Flocculated, Deflocculated

    Formulation of Suspensions: Particle Size Control

    • Particle size reduction is crucial for preventing sedimentation.
    • Stokes' law describes the relationship between settling velocity (v) and particle diameter (d): v = d² (p-po) g / 18η (where p is the density of the dispersed phase, po is the density of the medium, g is acceleration due to gravity, and η is viscosity).

    Physical Stability of Suspensions

    • Maintaining uniform distribution of particles in the dispersion medium is key to stability.
    • Particle size influences sedimentation rate (larger settle faster).
    • Fine particles can cake, while large are vulnerable to settling.

    Forces Acting on Particles

    • Gravity causes sedimentation.
    • Brownian movement counteracts sedimentation for particles less than 2-5 µm.

    Formulation Aspects of Suspensions

    • Ingredients: Insoluble drug, vehicle (suspending medium), wetting agents, compounds to control stability/sedimentation (flocculating/suspending agents), additives for flow behavior, pH regulators, other additives (flavor, color, preservatives).
    • Insoluble Drug: Particle size, size distribution, ease of wetting, interactions, surface charge are key considerations. Surface energy (AW = δSLΔA) increases with surface area.
    • Vehicle (suspending medium): Distilled water, water-alcohol, glycerol solutions, non-aqueous vehicles (topical use), structured vehicles.
    • Structured Vehicles: Contain compounds/polymers to form a three-dimensional network to minimize settling.

    Wetting Agents

    • Reduce surface tension of a liquid (e.g. water) so it penetrates a solid more easily.
    • Adsorbed air prevents liquids spreading on solid particles.
    • Wetting agents remove this air.

    Surfactants

    • Compounds which lower surface tension to facilitate wetting.
    • Polysorbates are non-ionic surfactants widely used.

    Hydrophilic Colloids

    • Coat hydrophobic drug particles.
    • Provide hydrophilic properties for easier wetting.
    • Often negatively charged, which can prevent agglomeration, but may decrease stability.

    Compounds Controlling Stability and Sedimentation

    • Suspending Agents/Viscosity Modifiers - Increase viscosity to reduce settling rate.
    • Thixotropy- Slow reversible conversion from gel(solid) to sol(fluid)- Viscosity decreases with agitation, allowing flow.

    Rheological Properties of Pharmaceutical Suspensions

    • Flow Characteristics: Ideal flow will be pseudoplastic or plastic, including the property of thixotropy (reversible conversion of gel to sol).

    Difference Between Flocculated and Deflocculated Suspensions

    • Flocculated: Particles form aggregates (flocs) that can redisperse easily. Higher sedimentation rate but sediment often easy to disrupt and redisperse.
    • Deflocculated: Particles remain individual entities. Lower sedimentation rate, potentially forming a hard cake.

    Other Additives

    • This includes buffering agents, flavorings, colorants, and preservatives.

    Evaluation of Suspensions

    • Sedimentation volume (F) - the ratio of sediment volume (Vu) to total volume (Vo). Quantifies the degree of sediment formation and evaluates the physical stability.
    • Degree of flocculation (B) - the ratio of sedimentation volume of flocculated to deflocculated suspension. Quantifies the degree of flocculation.

    Re-dispersability

    • number of inversions needed to redisperse a suspension.

    Preparation Steps

    1. Wetting and Dispersion of Active Ingredient
    2. Stabilization of Dispersed Solid
    3. Preparation of Vehicle (structured vehicle)
    4. Addition and Dispersion of Active Ingredient
    5. Addition of Remaining Ingredients, Final Mixing

    Packaging and Storage Of Suspensions

    • Wide mouth vessels to ensure uniform dosage.
    • Tight containers are protected from heat, light, and freezing.
    • Room temperature storage is usually sufficient, but refrigeration may be needed after opening or reconstitution

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    Description

    This quiz covers the fundamentals of suspensions in pharmacy, including their definitions, properties, and pharmaceutical applications. Understand the ideal characteristics of well-formulated suspensions and their role in drug delivery systems for poorly soluble drugs.

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