Suspension Definition, advantages and disadvantages

A  suspension is a dispersion of finely divided, insoluble solid particles (the disperse phase) in a fluid (the dispersion medium or continuous phase). 
A dispersed phase with a mean particle diameter of up to 1 um is usually termed a colloidal dispersion
A solid in liquid dispersion, in which the particles are above colloidal size, is termed a coarse suspension. 

Certain drugs are chemically unstable in solution but stable when suspended (ensures chemical stability while permitting liquid therapy.)
Ease of swallowing liquids and the flexibility in the administration of a range of doses
Overcome a disagreeable taste of certain drugs in solution form, when the drug is administered as undissolved particles of an oral suspension

1. Suspensions are a useful drug delivery system for therapeutic agents that have low solubility. Although low-solubility therapeutic agents may be solubilised and therefore administered as a solution, the volume of the solvent required to perform this may be large. In addition, formulations in which the drug has been solubilised using a co-solvent may exhibit precipitation issues upon storage.
2. Pharmaceutical suspensions may be formulated to mask the unpleasant/ bitter taste of the drug. E.g. Chloramphenicol.
3. Pharmaceutical suspensions may serve as an alternative means used to administer drugs to children including paediatric and geriatric patients and older patients who have difficulty swallowing solid dosage forms.
4. Drug in suspension exhibits a higher rate of bioavailability than other dosage forms. Bioavailability is in following order, Solution > Suspension > Capsule > Compressed Tablet > Coated tablet.
5. Pharmaceutical suspensions may be formulated to provide controlled drug delivery, e.g. as intramuscular injections.
6. Chemical stability of certain drugs e.g., Procaine penicillin G can be improved when formulated as suspensions.
7. Pharmaceutical suspension offers resistance to degradation of drugs due to hydrolysis, oxidation or microbial activity.
8. Duration and onset of action can be controlled e.g., Protamine Zinc-Insulin suspension.
9. When compared to solution dosage forms, relatively higher concentration of drugs can be incorporated into suspension products

1. Pharmaceutical suspensions are fundamentally unstable and for this reason, it requires formulation skill to ensure that the physical stability of the formulation is retained over the period of the shelf-life.
2. Aesthetic pharmaceutical suspension is difficult to formulate that is they lack elegance.
3. Accuracy of dosage is less reliable than with solution unless the suspension is packed in the unit dosage form.
4. Suspension formulations may be bulky and therefore difficult for a patient to carry.
5. Preparation must be shaken prior to measuring a dose.
6. Pourability and syringeability issues (e.g., injectable suspensions)
7. Crystal formation (Ostwald ripening) and breaking of suspension.