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

Why are electrolytes added during stabilization of dispersed solids?

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

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

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

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

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

What type of suspension is formulated primarily for parenteral use?

<p>Parenteral suspension (D)</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. (C)</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. (A)</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. (A)</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. (D)</p> Signup and view all the answers

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

<p>2 - 5 µm (C)</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 (D)</p> Signup and view all the answers

Which factor increases the flocculating power of electrolytes?

<p>The valency of the ions used. (B)</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. (A)</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. (A)</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 (A)</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 (A)</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 (D)</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 (B)</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. (D)</p> Signup and view all the answers

Structured vehicles in suspensions are designed primarily to do what?

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

Which of the following is a characteristic of deflocculated suspensions?

<p>Particles remain uniformly distributed longer. (D)</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. (B)</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. (C)</p> Signup and view all the answers

What is a characteristic of thixotropic compounds in structured vehicles?

<p>They decrease viscosity upon agitation (A)</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 (A)</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 (C)</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 (A)</p> Signup and view all the answers

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

<p>Flocculation starts to occur. (D)</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 (C)</p> Signup and view all the answers

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

<p>Glycerin solution (A)</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 (A)</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. (B)</p> Signup and view all the answers

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

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

How is wettability of a powder typically determined?

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

What characteristic should settled particles in a suspension have?

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

Which statement is true regarding the stability of suspensions?

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

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

<p>Greater wetting capability (C)</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 (A)</p> Signup and view all the answers

Flashcards

Zeta potential

Potential difference between the ions in the tightly bound layer and the electro-neutral region around a particle, affecting repulsion between similar charged particles in a suspension.

Counter ions

Oppositely charged ions near the potential-determining ions at the surface of a particle in a suspension.

Flocculation

Process where dispersed particles clump together to form larger, loose aggregates (floccules) due to reduced repulsion.

Electrolytes as flocculating agents

Electrolytes reduce the zeta potential by neutralizing the surface charge of particles, thus bringing them closer and leading to flocculation.

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Flocculating power

Ability of an electrolyte to cause flocculation, which increases with the valency of the ions.

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Surfactants as flocculating agents

Ionic or non-ionic surfactants can control flocculation by reducing surface tension between liquid and solid particles, drawing particles together.

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Rheological Properties (Suspensions)

The study of the flow and deformation characteristics of suspensions under different stress conditions.

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Flocculated Suspensions

Suspensions where particles clump together (flocculate) in clusters.

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Yield Value

The minimum stress required to initiate flow in a flocculated suspension.

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Plastic Flow

A flow behavior where a suspension requires a yield stress to begin flowing, then flows at a constant rate with increasing stress.

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Pseudoplastic Flow

The viscosity of a suspension decreases as the shear rate increases (thins out when stirred).

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Dilatant Flow

The viscosity of a suspension increases as the shear rate increases (gets thicker when stirred).

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Deflocculated Suspensions

Suspensions whose particles do not clump together and are evenly distributed.

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Wetting and Dispersion (Suspensions)

The process of distributing the active substance (drug) evenly throughout the liquid carrier.

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Stabilization of Dispersed Solid

Preventing the particles of the active substance from settling.

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Electrical Stabilization

Adding electrolytes to create charges on particles allowing them to repel and prevent aggregation.

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Preparation of Vehicle (Suspensions)

Making the liquid base for the suspension.

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Powder Dry Milling

Grinding powders to reach desired size & particle range.

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Suspension Definition

A liquid preparation with finely divided drug particles uniformly distributed in a vehicle.

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Suspension Particle Size Range

Solid particles in suspensions typically range from 0.5 to 5.0 microns.

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Ideal Suspension Properties

Particles should not settle, form hard cakes, redisperse easily, remain homogeneous, be free from grit, and have a pleasant/palatable taste and be stable.

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Suspension Applications (Oral)

Used to deliver insoluble or poorly soluble drugs orally (e.g., for children, elderly). Useful also when drugs are unstable in solution.

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Suspension Applications (Topical)

Liquid or semisolid preparations (pastes) for topical use; leave a deposit after evaporation.

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Flocculated Suspension

Suspension where particles clump together in loose aggregates (floccules).

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Deflocculated Suspension

Suspension where particles are evenly distributed.

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Suspension particle size

The size of particles in a suspension affects how quickly they settle.

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Stokes' Law

Mathematical formula describing the rate at which particles settle in a suspension. It relates settling velocity to particle size, density differences, and viscosity of the liquid.

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Brownian motion

Random movement of particles in a fluid as the result of collisions with other molecules. Brownian motion works to suspend the particles, preventing them from settling immediately.

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Parenteral suspension

A suspension administered by injection, used to control the rate of drug absorption.

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Oral suspension

A liquid medicine with solid particles suspended in a liquid that's taken by mouth.

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Colloidal suspension

A suspension with particles extremely small, typically less than one micron (1/1000 mm).

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Coarse suspension

A suspension with relatively large particles (greater than 1 micron) suspended in a liquid.

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Physical stability (of suspension)

Maintaining particles evenly distributed in a suspension over time.

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Insoluble drug

The substance that is not soluble in the liquid suspending medium.

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Suspending medium

Liquid that holds the insoluble drug in suspension

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Wetting agents

Substances that reduce surface tension between solid particles and liquid, making them mix well.

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Stability and Sedimentation Control

Substances added to prevent settling of particles in a suspension.

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Structured Vehicles

Vehicles with polymers/compounds that form a gel network, trapping particles to help with stability.

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Particle size

The dimension of the drug particles in a suspension.

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Sedimentation

The process where particles settle out of a suspension over time.

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Surface free energy

Energy associated with the surface area of a substance.

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Hydrophobic Powders

Powders that do not readily wet with water, like sulfur and magnesium stearate.

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Hydrophilic Powders

Powders that readily wet with water, an example is zinc oxide.

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Contact Angle

The angle where a liquid meets a solid surface.

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Wetting Agent

A substance that promotes the wetting of a surface by a liquid.

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Surfactant Example

Polysorbate 80 is a non-ionic surfactant.

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Spreading Coefficient

A measure of how easily a liquid spreads on a solid surface.

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Surface Tension of a Solid

The force that holds the solid surface together, measured in 𝛿S.

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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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