Learning Objective

• Incompatibility and its different types

Incompatibility may be defined as mixing two or more antagonistic substances resulting in an undesirable product, which may affect the safety, efficacy and appearance of the preparation.

There are three types of incompatibilities:

1. Physical incompatibilities: When two or more antagonistic substances are combined together, a physical change takes place and an unacceptable product is formed due to immiscibility, insolubility or liquefaction. The changes are visible and can be corrected by an application of pharmaceutical skill to obtain a product of a uniform dosage and an attractive appearance.
2. Chemical incompatibilities: These are caused by pH changes, complex formation, oxidation–reduction, hydrolysis or combination reactions. These reactions are noticed by precipitation, effervescence, decomposition, color change or explosion.
3. Therapeutic incompatibilities: These may be as a result of prescribing certain drugs to a patient with an intention to produce a specific degree of pharmacological action, but the nature or intensity of action produced is different from that intended by the prescriber.