PHARMACEUTICAL SUSPENSIONS

DISPERSE SYSTEM

—The term "Disperse System" refers to a system in which one substance (The Dispersed Phase) is distributed, in discrete units, throughout a second substance (the continuous Phase ).

—

—Each phase can exist in solid, liquid, or gaseous state .

—Suspensions are heterogenous system consisting of 2 phases.

   Definition

Ø   A Pharmaceutical suspension is a  coarse dispersion in which internal

      phase (therapeutically active ingredient)is dispersed uniformly

      throughout the external phase.

ØThe internal phase consisting of insoluble solid particles  

     having a range of size(0.5 to 5 microns) which is  maintained uniformly through out the suspending vehicle with aid of single or combination of suspending agent.

Ø The external phase (suspending medium) is generally
 aqueous in some instance, may be an organic or oily  liquid for non oral use.

The reasons for the formulation of a pharmaceutical suspension:

-- when the drug is insoluble in the delivery vehicle.

–To mask the bitter taste of the drug.

–To increase drug stability.

–To achieve controlled/sustained drug release.

SOME PHARMACEUTICAL SUSPENSIONS

—1. Antacid oral suspensions

—2. Antibacterial oral suspension

—3. Dry powders for oral suspension (antibiotic)

—4. Analgesic oral suspension

—5. Anthelmentic oral suspension

—6. Anticonvulsant oral suspension

—7. Antifungal oral suspension

Classification

Based On General Classes

Ø Oral suspension

     eg: Paracetamol suspension

       antacids, Tetracycline HCl.

Ø  Externally applied suspension

      eg :Calamine lotion.

Ø  Parenteral suspension

eg: Procaine penicillin G

Insulin Zinc Suspension

Based on Proportion of Solid Particles

Ø  Dilute suspension (2 to10%w/v solid)

Eg: cortisone acetate, predinisolone acetate

Ø  Concentrated suspension (50%w/v solid)

Eg: zinc oxide suspension

 Based on Electrokinetic Nature of Solid Particles

Ø Flocculated suspension

Ø Deflocculated suspension

Based on Size of Solid Particles

ØColloidal suspensions (< 1 micron)

-Suspensions having particle sizes of suspended solid less than about 1micron in size are called as colloidal suspensions.

Coarse suspensions (>1 micron)

ØSuspensions having particle sizes of greater than about 1micron in diameter are called as coarse suspensions.

Nano suspensions (10 ng)

Ø Suspensions are the biphasic colloidal dispersions of nanosized drug particles stabilized by surfactants.

ØSize of the drug particles is less than 1mm.

Advantages And Disadvantages

ADVANTAGES

Suspension can improve chemical stability of certain drug.

  E.g. Procaine penicillin G.

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

Solution > Suspension > Capsule > Compressed Tablet > Coated tablet

ØDuration and onset of action can be controlled.

    E.g. Protamine Zinc-Insulin suspension.

ØSuspension can mask the unpleasant/ bitter taste of drug.

    E.g. Chloramphenicol

DISADVANTAGES

ØPhysical stability , sedimentation and compaction can causes 

     problems.

Ø It is bulky sufficient care must be taken during handling and 

    transport.

Ø It is difficult to formulate.

Ø Uniform and accurate dose can not be achieved unless suspension are  packed in unit dosage form.

Applications

Ø  Suspension is usually applicable for drug which is insoluble

     (or )   poorly soluble.

    E.g. Prednisolone suspension

Ø  To prevent degradation of drug or to improve stability of drug.

     E.g. Oxy tetracycline suspension

Ø  To mask the taste of bitter of unpleasant drug.
      E.g. Chloramphenicol  palmitate suspension

Ø  Suspension of drug can be formulated for topical application  

     e.g. Calamine lotion

ØSuspension can be formulated for parentral application in order to

    control rate of drug absorption. E.g. penicillin procaine

Ø Vaccines as a immunizing agent are often formulated as suspension.
     E.g. Cholera vaccine

Ø  X-ray contrast agent are also formulated as suspension .

     eg: Barium sulphate for examination of alimentary tract.