Pharmaceutical Suspensions Overview

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What are the desirable criteria for a suspension to be effective?

The suspended material should not settle too rapidly, should not form a hard cake when settled, should disperse into a uniform mixture easily, and must not be too viscous.

In what forms can suspensions be utilized for pharmaceutical applications?

Suspensions can be used for oral, topical, parenteral, and pulmonary applications.

How do suspensions assist in drug delivery for patients who have difficulty swallowing?

Suspensions provide an alternative dosage form that is easier to take compared to solid dosage forms.

Why are vaccines sometimes formulated as suspensions?

Vaccines are formulated as suspensions to prolong the antigenic stimulus and achieve a high antibody titre. Signup and view all the answers

What is a key stability concern for suspensions compared to solutions?

Stability is a concern due to potential degradation in water, which can affect the overall formulation and efficacy. Signup and view all the answers

What is the role of adsorbed layers in stabilizing pharmaceutical suspensions?

Adsorbed layers hinder the close approach of particle surfaces, preventing aggregation and maintaining stability. Signup and view all the answers

How do natural and synthetic stabilizers affect the viscosity of suspensions?

They increase the viscosity of the aqueous vehicle, which slows down the sedimentation rate of particles. Signup and view all the answers

What is the difference between flocculated and deflocculated suspensions?

Flocculated suspensions have loosely bonded particle aggregates, while deflocculated suspensions consist of separate entities with low bonding. Signup and view all the answers

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

Smaller particle sizes result in a slower sedimentation rate, while larger particle sizes, especially over 25 µm, can lead to problems like grittiness. Signup and view all the answers

What kind of flow properties do flocculated and deflocculated systems exhibit?

Flocculated systems exhibit plastic or pseudoplastic flow, whereas deflocculated systems show Newtonian flow behavior. Signup and view all the answers

Study Notes

Introduction to Suspensions

A suspension is a coarse dispersion of insoluble particles greater than 1 µm in diameter in a liquid medium, usually aqueous.
Common uses include administering insoluble or poorly soluble drugs orally, parenterally, ophthalmically, and dermatologically.
Suspensions differ from colloids due to particle size differences.

Desirable Criteria for Suspensions

The suspended material should not settle too quickly.
Settled particles should not form a hard cake.
The mixture should readily disperse into a uniform mixture when shaken.
The suspension should be pourable and flowable, avoiding excessive viscosity.

Pharmaceutical Applications of Suspensions

Oral: Suitable for administering drugs difficult to be swallowed as solid dosage forms.
Topical: Used for skin and mucous membrane applications in fluid or semi-solid forms.
Parenteral: Injectable suspensions can control drug activity duration.
Pulmonary: Can be used in inhalation therapies.

Suspensions as Oral Drug Delivery Systems

Difficulty in swallowing solid dosage forms: Formulations overcome this issue.
Adsorption of toxins (e.g., Kaolin): Kaolin and other substances can adsorb toxins or neutralize excess acidity.
Taste of drugs: Suspensions can mask unpleasant tastes of active medications compared to solid forms.

Suspensions for Topical Administration

Fluid preparations: Like calamine lotion, often depositing after solvent evaporation.
Semisolid preparations (pastes): High concentrations of powders are present.
Emulsion bases (e.g., zinc oxide creams): Formulations often make use of pre-existing emulsion bases.

Suspensions for Parenteral Use and Inhalation Therapy

Controlled activity duration: Dissolution rates can be manipulated to control drug activity.
Suspension in oil (injections): A suspension in oil can control the rate of absorption.
Vaccines: Killed microorganisms or toxoids on aluminum substrates achieve a prolonged antigenic stimulus and high antibody titer.
X-ray contrast media: These suspensions frequently use barium sulfate.

Stability of Suspensions: Solubility Aspects

Water and Degradation: Water can increase degradation in some suspensions, impacting stability.
Insoluble vs. Soluble Derivatives: Creating an insoluble derivative from a soluble form can improve suspension stability.
Reconstitution: Preparation for injection requires reconstitution of powder formulations, altering stability.

Steric Stabilization of Suspensions

Adsorbed Layers: Stabilizing particles by using materials to create adsorbed layers around particles and prevents aggregation.
Dispersants: Dispersants with anchoring groups and soluble tails are critical components for adsorption.
Control of Agglomeration: Formation of layers hinders aggregation to prevent coagulation.

Steric Stabilization of Suspensions: Natural and Synthetic Materials

Natural materials (e.g., gum tragacanth): Used in stabilizing suspensions.
Synthetic materials (e.g., non-ionic surfactants and cellulose polymers): Contribute to stabilizing suspensions.
Viscosity and Sedimentation: Adsorbed layers and stabilizers increase viscosity and reduce sedimentation rates, improving stability.

Caking and Flocculation in Suspensions

Sedimentation and Caking: Under sedimentation, particles lose their repulsive barrier, leading to close particle packing, eventually causing caking.
Flocculation: If electrolytes are incorporated, charges accumulate causing loose particle bonding resulting in flocculation.
Deflocculated and Flocculated Suspension visualization: An illustration depicts two types of suspensions: deflocculated (more dispersed) and flocculated (less dispersed).
Comparison of flocculated and non-flocculated suspensions: Comparison table with key differences in flocculated and Non-flocculated systems regarding rate of sedimentation and quality of sediment.

Rheology of Suspensions

Low Shear Rates: High viscosity slows down particle sedimentation and enhances stability.
High Shear Rates (Shaking): Decreased viscosity allows for easier dispersion and administration.
Flow Behavior: Flocculated systems exhibit plastic or pseudoplastic flow characteristics, whereas deflocculated systems exhibit Newtonian-like behavior.

Formulation of Suspensions: Particle Size Control

Particle Size (P.S.): Smaller particle sizes lead to reduced sedimentation rates.
Grit, Blocking: Larger particle sizes result in grittiness and can block syringe needles.
Dissolution Rate: Particle size strongly influences the dissolution rate of the drug in the suspension.

Formulation of Suspensions: Wetting Agents

Hydrophobicity and Wetting: Insoluble solids often exhibit reduced wetting by liquid media due to hydrophobicity.
Interfacial Tension: Lowering interfacial tension through surface active agents (e.g., Tweens, Spans) enhances wetting.
HLB Values: Choosing surface-active agents with appropriate HLB (Hydrophilic-Lipophilic Balance) values is crucial for optimal wetting.

Formulation of Suspensions: Hydrophilic Colloids

Protective Layers: Coatings of hydrophilic colloids can stabilize suspensions by creating layers of protection on hydrophobic particles.
Suspending Agents: Acacia, bentonite, tragacanth, alginates, xanthan gum, and cellulose derivatives serve as suspending agents.
Stabilization: Hydrophilic colloids improve suspension stability.

Formulation of Suspensions: Solvents

Miscibility: Solvents like alcohol, glycerol, and glycols, which are miscible with water, lower the interfacial tension between solid and liquid phases.
Interfacial Tension Reduction: Lowering interfacial tension promotes better dispersion and suspension stability.

Formulation of Suspensions: Flocculating Agents

Electrolytes: Electrolytes can alter the zeta potential of dispersed particles to cause or assist in flocculation.
Surfactants: Ionic surfactants often cause flocculation, while non-ionic can produce loose flocculated structures.
Polymeric agents: Polymers form gel-like networks that adsorb onto particle surfaces, holding them firmly in a flocculated state.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz explores the fundamentals of suspensions, focusing on their characteristics, desirable criteria, and applications in pharmaceuticals. Gain insights into various forms of suspensions used for drug administration and the importance of particle size. Perfect for students in pharmaceutical sciences.