A Review on Stability of Drugs and Pharmaceutical Dosage Form

The stability of a pharmaceutical product is a multifaceted concept that guarantees the maintenance of quality, safety, and efficacy throughout its intended shelf life. At its core, stability refers to the duration a dosage form remains within acceptable limits before it begins to degrade, which ultimately determines the product’s expiration date. This degradation is governed by chemical kinetics, specifically the order of reaction, which describes how the concentration of reactants—such as the Active Pharmaceutical Ingredient (API)—influences the rate of breakdown. For instance, while zero-order reactions proceed at a rate independent of concentration, most pharmaceutical degradation follows first-order kinetics, where the rate is directly proportional to the drug's remaining concentration. These chemical processes are often driven by specific mechanisms, most notably oxidation and hydrolysis. Oxidation is considered the most significant pathway, as atmospheric oxygen can decompose substances not in their most oxidized state. Hydrolysis is equally prevalent, occurring when water performs nucleophilic attacks on labile bonds, particularly in lactam groups, esters, and amides. Beyond chemical integrity, stability is classified into several critical categories, including physical, microbiological, therapeutic, and toxicological stability. Physical stability ensures the product retains its original appearance, color, and dissolution properties, while microbiological stability prevents harmful microbial growth and maintains the efficacy of added preservatives. These characteristics are heavily influenced by environmental factors such as temperature, humidity, and light. Higher temperatures generally accelerate hydrolytic reactions, and exposure to light can cause rapid degradation in photosensitive medications, necessitating specialized packaging like amber glass bottles. Furthermore, product-related factors, such as the water content of excipients like starch or the nature of the container closure system, play a pivotal role in maintaining the API's integrity.