Oxidation is the second most common degradation pathway for pharmaceuticals, after hydrolysis. However, in contrast to hydrolysis, oxidation is mechanistically more complex and produces a wider range of degradation products; oxidation is thus harder to control. The propensity of a drug towards oxidation is established during forced degradation studies. However, a more realistic insight into degradation in the solid state can be achieved with accelerated studies of mixtures of drugs and excipients, as the excipients are the most common sources of impurities that have the potential to initiate oxidation of a solid drug product. Based on the results of these studies, critical parameters can be identified and appropriate measures can be taken to avoid the problems that oxidation poses to the quality of a drug product. This article reviews the most common types of oxidation mechanisms, possible sources of reactive oxygen species, and how to minimize the oxidation of a solid drug product based on a well-planned accelerated study.

Famotidine, a widely used H ₂ -receptor antagonist, exhibits sensitivity to oxidative degradation, particularly in the presence of excipients containing peroxide impurities. This study explores the oxidative stability of famotidine under various storage conditions, with a specific focus on excipients with varying peroxide contents. A stability-indicating liquid chromatography-mass spectrometry (LC-MS) method was developed to identify and quantify famotidine degradation products, providing detailed insights into oxidative pathways. In addition, Zeneth software was employed to predict potential degradation products, and its predictive accuracy was evaluated against experimental findings. Antioxidants, including ascorbic acid, propyl gallate, and ethylenediaminetetraacetic acid (EDTA), were incorporated into compressed compatibility mixtures to assess their effects on peroxide-mediated degradation. While propyl gallate and EDTA consistently reduced peroxide levels and enhanced stability, ascorbic acid unexpectedly acted as a pro-oxidant under stress conditions, accelerating peroxide formation in povidone. These findings provide critical insights into mitigating oxidative degradation in famotidine and other solid dosage forms, emphasizing the importance of selecting appropriate excipients, antioxidants, and predictive tools to ensure product stability.