Chemical kinetics and stability

Chemical kinetics and stability

Introduction

Drug substances and drug products are required to be physically and chemically stable under recommended storage conditions to maintain their identity, potency, and safety throughout the shelf life. Most drugs are sus-ceptible to chemical decomposition in their dosage forms. Degradation can lead to loss of the drug’s potency and generation of impurities in drug products. Regulatory agencies, such as the Food and Drug Administration (FDA), require identification, quantitation, and/or toxicological evaluation of impurities in drug products when they exceed a given threshold, which depends on the drug’s daily dose. In addition to the time and cost associ-ated with these investigations, if an impurity is found to be significantly toxic, it can compromise a drug development program. Understanding of the rates and mechanisms of drug degradation reactions and implementing stabilization strategies help identify strategies to control the extent of formation of impurities in drug products. For example, the knowledge of the rate at which a drug deteriorates under various conditions of pH, tem-perature, humidity, and light allows formulators to choose a vehicle that will retard or prevent drug degradation.

Chemical kinetics deals with rates of chemical reactions. A knowledge of reaction kinetics under various conditions helps identify mechanisms of drug degradation and stabilization.