ABSTRACT
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. Chemical kinetics deals with rates of chemical reactions. A knowledge of reaction kinetics under various conditions helps identify mechanisms of drug degradation and stabilization. For hydrolytically sensitive drugs, water acts as a reactant and increases the drug degradation rate directly by participating in a bimolecular reaction. Such reactions may follow second-order or pseudo first-order kinetics, depending on whether water is available in the reaction medium in limited or ample quantity. A drug undergoes more than one chemical reaction or a series of reactions in the same environment. Such complex reactions can be exemplified by reversible, parallel, or consecutive reactions. The effect of temperature on the rate of drug degradation is expressed in terms of the effect of temperature on the reaction rate constant by the Arrhenius equation.
