General Considerations Modes of Drug Decomposition Drug–excipient Interactions

Excipients are included in dosage forms to aid manufacture, administration or absorption. Other reasons for inclusion concern product differentiation, appearance enhancement or retention of quality.1 They rarely, if ever, possess pharmacological activity and are accordingly loosely categorized as ‘inert.’ However, excipients can initiate, propagate or participate in chemical or physical interactions with an active, possibly leading to compromised quality or performance of the medication. Chemical interaction can lead to degradation of the active ingredient, thereby reducing the amount available for therapeutic effect; reaction products may compromise safety or tolerance. Physical interactions can affect rate of dissolution, uniformity of dose or ease of administration. Understanding the chemical and physical nature of excipients, the impurities or residues associated with them and how they may interact with other materials, or with each other, forewarns the pharmaceutical technologist of possibilities for undesirable developments.