Pharmaceutical suspension

Faysal Ahmed

Id:151-29-760

A Pharmaceutical suspension is a disperse system in which internal phase is

dispersed uniformly as finely divided insoluble particles throughout the

external phase.

Suspension

The Difference Between Solution & Suspensions:

When the 2 substances totally mix it is called a solution.

E.g. Solute + Solvent = Solution

(sugar) + (water) = Solution

We then say sugar is soluble in water, it has dissolved.

The particles in a suspension are insoluble

Sometimes when we mix substances they stay in clusters. We therefore say it is

insoluble in water.

E.g. Chalk + Water = Suspension

Eventually the particles sink to the bottom to form sediment.

Types of pharmaceutical suspensions:

Antacid oral suspensions

Antibacterial oral suspension

Dry powders for oral suspension (antibiotic)

Analgesic oral suspension

Anthelmentic oral suspension

Anticonvulsant oral suspension

Antifungal oral suspension

Classification:

Based on General Classes :

Oral suspension

Externally applied suspension

Parenteral suspension

Based on Proportion of Solid Particles:

Dilute suspension (2 to10%w/v solid)

Concentrated suspension (50%w/v solid)

Based on Electro kinetic Nature of Solid Particles:

Flocculated suspension

Deflocculated suspension

Based on Size of Solid Particles:

Colloidal suspension (< 1 micron)

Coarse suspension (>1 micron)

Nano suspension (10 ng)

Formulating Consideration of Suspensions:

Wetting agents

Particle Size

Particle shape

Particle- particle Interaction

Suspending agent

Wetting agent:

A substance is referred to as a wetting agent if it lowers the surface tension of a liquid

and thus allows it to spread more easily.

It is the important factor to be considered for formulation of suspension because the

more the wetable particle the more stable the suspension.

Wetting ability depends upon the angle of contact between the particle and the solvent

which should be less than 90 C.

e.g: Polysorbate 80 etc.

Particle size:

It is critical part to be considered and the particle size must be reduced within the range.

Too large or too small particles should be avoided.

Large particles settle down faster.

Smaller particles may form agglomerates.

Required particles size maintained to form stable suspension.

Particle shape:

Spherical shape particles form the more viscous with low rate of sedimentation

of suspension that's why it is preferable over needle shaped particles.

Particle- Particle Interaction:

A. Zeta potential

B. Deflocculation and

C. Flocculation.

The zeta potential is defined as "the difference in potential between the surface of

tightly bound layer."

If the zeta potential is reduced, the attractive forces exceed the repulsive forces and the

particles come together, this phenomena is known as flocculation

B. Flocculated Suspension:

In flocculated suspension, formed flocs i.e. loose aggregates will increase in

sedimentation rate due to increase in size of sedimenting particeles.It also depends

upon the porosity of flocs.

C. Deflocculated Suspension:

In this, individual particles are settling, rate of sedimentation is slow, which prevents

entrapping of liquid medium which makes it difficult to redisperse by agitation. This

phenomena known as caking.

The larger particles settle fast and smaller remain in supernatant so supernatent appears

cloudy.

Suspending agent:

They form film around particle and decrease the interparticle attraction.

They also imparts viscosity to the solution.

Examples: Sodium alginates, Methylcellulose, CMC, silicon dioxide etc.

Reasons for the formulation of a suspension:

when the drug is insoluble in the delivery vehicle.

To mask the bitter taste of the drug.

To increase drug stability.

To achieve sustained drug release.

Quality Control of Suspensions:

Appearance Color, odor and taste

Sedimentation rate and

Zeta Potential measurement

Sedimentation volume

pH

Redispersibility and Centrifugation tests

Rheological measurement

Stress test

Advantages of Suspension:

Suspension can improve chemical stability of certain drug. E.g. Procaine penicillin G

Drug in suspension exhibits higher rate of bioavailability than other dosage forms.

Bioavailability is in following order:

Solution > Suspension > Capsule > Compressed Tablet > Coated tablet

Duration and onset of action can be controlled. E.g. Protamine Zinc-Insulin

suspension

Suspension can mask the unpleasant/ bitter taste of drug. E.g. Chloramphenicol

palmitate

Disadvantages of Suspension:

Physical stability, sedimentation and compaction can causes problems.

It is bulky, therefore sufficient care must be taken during handling and transport.

It is difficult to formulate.

Uniform and accurate dose can not be achieved unless suspension are packed in

unit dosage form .

Pharmaceutical Application of suspension:

Suspension is usually applicable for drug which is insoluble or poorly soluble.

E.G. Prednisolone

Suspension to prevent degradation of drug or to improve stability of drug. E.G.

Ox tetracycline suspension

To mask the taste of bitter of unpleasant drug. E.G. Chloramphenicol

palmitate suspension

Suspension of drug can be formulated for topical application E.G. Calamine

lotion.