Definition of Suspension Pharmaceutical Liquid Dosage Form

A Pharmaceutical suspension is a coarse dispersion in which internal phase is dispersed uniformly throughout the external phase. The internal phase consisting of insoluble solid particles having a specific range of size which is maintained uniformly through out the suspending vehicle with aid of single or combination of suspending agent. The external phase (suspending medium) is generally aqueous in some instance, may be an organic or oily liquid for non oral use.

or

Suspension is a preparation containing the solid ingredients in the form of subtle and not soluble, dispersed in a liquid carrier. Substances dispersed should be fine, should not be quick to settle, and when shake slowly, the precipitate should be dispersed again. Additives may be added to ensure the stability of the suspension but the suspension viscosity must ensure the preparation easy to shake and pour.

Some suspensions are prepared and ready for use, while others are prepared as solid mixtures intended for constitution just before use with an appropriate vehicle.

In the manufacture of suspension must be considered some factors, among other :
  • the nature of the dispersed particles (degree of wetting of particles)
  • wetting agent
  • dispersing medium
  • other components such as dyes, flavoring and preservatives used.
The suspension must be packed in appropriate containers above the liquid so it can easily shaken and poured. On the label must be printed "Shake and stored in closed and cool place".



Classification of Suspension 

Based On General Classes
• Oral suspension
• Externally applied suspension : Topical suspensions, Otic Suspension, Ophtalmic suspensions
• Parenteral suspension

Based on Proportion of Solid Particles
• Dilute suspension (2 to10%w/v solid)
• Concentrated suspension (50%w/v solid)

Based on Electrokinetic 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)


Advantages and Disadvantages of Suspension as Pharmaceutical Dosage Form

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

Disadvantages of Suspension
  • Physical stability, sedimentation and compaction can causes problems.
  • Susceptible to degradation and the possibility of chemical reaction between the ingredients in the solution where there is water as a catalyst.
  • It is bulky sufficient care must be taken during handling and transport.
  • It is difficult to formulate
  • Uniform and accurate dose cannot be achieved unless suspension are packed in unit dosage form

Good and Desired Properties of Pharmaceutical Suspensions
  • The suspended particles should not settle rapidly and sediment produced, must be easily re-suspended by the use of moderate amount of shaking.
  • It should be easy to pour yet not watery and no grittiness.
  • It should have pleasing odour, colour and palatability.
  • Good syringeability.
  • It should be physically, chemically and microbiologically stable.
  • Parenteral/Ophthalmic suspension should be sterilizable.

Why Choose Suspensions as Pharmaceutical Dosage Form?

The Applications of suspensions:
  • Suspension is usually applicable for drug which is insoluble or poorly soluble (Prednisolone suspension)
  • To prevent degradation of drug or to improve stability of drug. (Oxytetracycline suspension)
  • To mask the taste of bitter of unpleasant drug. (Chloramphenicol palmitate suspension)
  • Suspension of drug can be formulated for topical application (Calamine lotion)
  • Suspension can be formulated for parentral application in order to control rate of drug absorption.
  • Vaccines as a immunizing agent are often formulated as suspension (Cholera vaccine)
  • X-ray contrast agent are also formulated as suspension. (Barium sulphate for examination of alimentary trac)

Search