Pharmaceutical Suspensions Overview

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Questions and Answers

What role do adsorbed layers play in the stabilization of pharmaceutical suspensions?

They increase the sedimentation rate of particles.

They hinder the approach of particle surfaces and aggregation. (correct)

They facilitate electrostatic attraction between particles.

They promote the caking of particles.

Which of the following materials may be used for steric stabilization of suspensions?

Natural gums and synthetic surfactants (correct)

Alcohol-based solvents

Electrolytes

Water

What is the primary effect of adding electrolytes to a suspension?

Enhance the caking of particles.

Encourage loose bonding between particles. (correct)

Increase the viscosity of the suspension.

Create a repulsive barrier between particles.

What characteristic describes deflocculated suspensions compared to flocculated suspensions?

Particles exist as separate entities. Signup and view all the answers

Which flow characteristic is associated with flocculated systems?

Pseudoplastic flow Signup and view all the answers

What is the impact of particle size on the sedimentation rate of suspensions?

Larger particles sediment faster. Signup and view all the answers

What happens to the viscosity of a suspension at high shear rates?

It decreases, facilitating easier administration. Signup and view all the answers

What is a key characteristic of particles in a suspension?

They are dispersed in a liquid medium, generally greater than 1 micron. Signup and view all the answers

Which of the following is NOT a desirable criterion for a suspension?

The suspended material should settle rapidly. Signup and view all the answers

What type of administration can suspensions be used for?

Oral, parenteral, and inhalation therapy. Signup and view all the answers

Which statement about suspensions for topical administration is true?

They can be fluid or semisolid preparations. Signup and view all the answers

How can the duration of activity of a parenteral suspension be controlled?

By manipulating the dissolution rate. Signup and view all the answers

What is a common use of suspensions in vaccination?

To adsorb killed microorganisms on a substrate. Signup and view all the answers

Which factor impacts the stability of suspensions?

The solubility of the drug. Signup and view all the answers

What type of vehicle can be used for the reconstitution of certain drugs in suspensions?

Fractionated coconut oil. Signup and view all the answers

Study Notes

Introduction to Suspensions

A suspension is a coarse dispersion of insoluble particles (generally larger than 1 µm in diameter) in a liquid medium (usually aqueous).
Suspensions are useful for administering insoluble or poorly soluble drugs.
They can be used for oral, parenteral, ophthalmic, and dermatological applications.
Suspensions are different from colloids.

Desirable Criteria for Suspensions

The suspended material should not settle too quickly.
Settled particles should not form a hard cake at the bottom of the container.
The mixture should readily disperse into a uniform mixture when the container is shaken.
The suspension should not be too viscous to pour freely from the bottle or flow through a syringe needle.

Pharmaceutical Applications of Suspensions

Oral administration
Topical administration (skin or mucous membranes)
Parenteral administration (injection)
Pulmonary administration (inhalation)

Suspensions as Oral Drug Delivery Systems

Difficulty in swallowing solid dosage forms is a reason to use suspensions.
Some suspensions are used to absorb toxins (e.g., kaolin).
Others are used to neutralize excess acidity (e.g., magnesium carbonate, magnesium trisilicate).
Taste is a factor in choosing between different formulations (e.g., paracetamol solution vs. suspension, chloramphenicol vs. chloramphenicol palmitate).

Suspensions for Topical Administration

Fluid preparations like calamine lotions are frequently used.
These are often formulated to release the medication after the solvent evaporates.
Semi-solid preparations (such as pastes) contain high concentrations of powders.
Suspensions are also often incorporated into emulsion bases (e.g., zinc oxide creams).

Suspensions for Parenteral Use and Inhalation Therapy

Controlled release is a benefit of some suspensions.
The duration of activity can be regulated by controlling the dissolution rate (e.g., suspension in oil).
Suspensions in oil, for example, tend to have a slower dissolution rate and a more controlled absorption compared to water-based suspensions.
Vaccines are sometimes administered as suspensions of killed microorganisms, adsorbed on aluminum hydroxide or phosphate, leading to a prolonged antigenic stimulus and a higher antibody titre.
X-ray contrast media (e.g., barium sulphate) can be administered orally or rectally as suspensions.

Stability of Suspensions - Solubility Aspects

Water can cause degradation of the drug, leading to a loss of suspension stability, as compared to a solution.
Preparing an insoluble derivative of a soluble drug can improve its suspension stability.
Reconstitution procedures (e.g., with amoxicillin) can influence suspension stability.
Non-aqueous vehicles, like fractionated coconut oil, can improve stability.

Steric Stabilization of Suspensions

Adding materials to form adsorbed layers around particles prevents aggregation, therefore improving suspension stability.
These materials can also improve viscosity and slow sedimentation.

Steric Stabilization of Suspensions - Specific examples

Natural materials like gum tragacanth and synthetic materials like non-ionic surfactants and cellulose polymers are used to stabilize suspensions.

Caking and Flocculation

During sedimentation, particles can form bridges, leading to compaction (caking).
Adding electrolytes can cause charge accumulation, leading to loose bonding and flocculation.
Deflocculated suspensions allow for individual particles, while flocculated suspensions have agglomerated particles. Flocculated suspensions sediment quicker and may be easier to redisperse.

Rheology of Suspensions

At low shear rates, suspensions show high viscosity and reduced sedimentation.
High shear rates (like shaking) reduce the viscosity, simplifying administration.
Flocculated suspensions exhibit plastic or pseudo-plastic flow.
Deflocculated suspensions exhibit Newtonian flow.

Formulation of Suspensions - Particle Size Control

Smaller particle size reduces sedimentation rate and prevents grittiness or syringe blockage.
Particle size controls the dissolution rate.

Formulation of Suspensions - Wetting Agents

Insoluble solids often have varying degrees of hydrophobicity making them harder to wet.
Wetting agents like surface-active agents (HLB 7-9) reduce interfacial tension, facilitating complete wetting.
Tweens and spans are common wetting agents for oral use.

Formulation of Suspensions - Other Considerations

Sodium lauryl sulphate, sodium dioctyl sulphosuccinate are used as wetting agents for topical use.
Tweens, poloxamers and lecithin are commonly used for parenteral applications.
Hydrophilic colloids (e.g., acacia, bentonite, tragacanth) coat hydrophobic particles and prevent flocculation/aggregation.
Alcohol, glycerol, and glycols are solvents that lower interfacial tension in suspensions.
Electrolytes can influence the zeta potential of particles and promote flocculation.
Surfactants can either cause flocculation or promote the formation of a loose aggregation (flocculation) structure depending on their properties.
Polymeric flocculating agents (e.g., starch, alginates, cellulose derivatives) create a gel-like network around the particles, helping them remain suspended in a flocculated state.

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Description

This quiz covers the fundamentals of suspensions, emphasizing their characteristics and desirable criteria for pharmaceutical applications. Learn how suspensions serve critical roles in oral and parenteral drug delivery, along with their use in topical and pulmonary administration. Understand the differences between suspensions and colloids to enhance your knowledge in pharmaceutical sciences.