Excipient Compatibility

Publisher Summary The excipient compatibility is related to the physical and chemical stability of the drug in solid dosage forms. Some of the common ways by which excipients may affect drug stability in the dosage form are by altering moisture content in the dosage form, changing microenvironmental pH in the dosage form, acting as general acid–base catalysts, directly reacting with drug or becoming a source of impurities that can either directly react with drug substances or participate as catalysts in the drug degradation. The excipients can also alter the physical and/or the chemical form of the drug through, for example, ion-exchange, transformation of polymorphs, and the formation of eutectic or solid solutions. The changes in physical or chemical state may in turn alter the chemical stability of the drug. Most drugs and excipients contain water, which may be either bound or unbound. The physical state of water in an excipient or the drug–excipient mixture determines its potential role in drug–excipient interactions. Presence of water in the solid-state systems has a significant impact on the stability, not only in causing the hydrolysis of drugs, e.g., of acetylsalicylic acid, but also its participation as a reaction medium, and in increasing the plasticity and molecular mobility of the system.