Pharmaceutical suspension is a liquid dosage form containing finely divided, undissolved drug particles dispersed throughout a liquid vehicle in which the drug exhibits a minimum degree of solubility. This dosage form is used for providing a liquid dosage form for insoluble drugs.
In an ideal suspension, particles are uniformly dispersed and remain so even after prolonged periods of time. Even if sedimentation occurs, particles should readily redisperse upon mild agitation of the container.
Suspensions have a number of therapeutic applications across different routes of administration. Most suspensions are available in ready-to-use form from the manufacturer. In cases of physical or chemical incompatibility, they are marketed as reconstitutable medications in unit-dose sachet or multidose bottles.
Read Also: How to Reconstitute Oral Suspension
This article focuses on the advantages and disadvantages of pharmaceutical suspensions
The following advantages can be obtained by formulating API as a suspension dosage form.
1. Suspensions are a useful drug delivery system for therapeutic agents that have a 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 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 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.
The disadvantages of suspensions as pharmaceutical products include the following:
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 suspension is packed in 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.
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