Drug stability designates the capacity of a pharmaceutical substance or dosage form, within specified limits and throughout its period of storage and use, to retain the same properties and characteristics that it possessed at the time of manufacture. The concept is operationally partitioned into chemical stability, in which each active ingredient retains its chemical integrity and labelled potency, and physical stability, in which the original physical properties—appearance, uniformity, dissolution, and suspendability—are preserved ^[1]. Chemical degradation proceeds through defined pathways whose relative contributions depend on the molecular structure and the formulation environment: hydrolysis of ester, amide, and lactam bonds is accelerated by moisture and adverse pH; oxidation involves reaction with molecular oxygen and is promoted by trace metals, light, and elevated temperature; photolysis results from absorption of ultraviolet or visible radiation; and epimerization, isomerization, and polymerization constitute further routes of chemical change ^[2]. The environmental factors that reduce stability include temperature, light, humidity, oxygen, and carbon dioxide, while the dosage-form factors include particle size, pH, solvent composition, ionic strength, container, and excipient compatibility ^[1]. The term therefore denotes the property of a formulated pharmaceutical product—defined by its chemical and physical integrity under defined storage conditions—together with the degradation mechanisms and formulation variables that determine the shelf-life within which that integrity is maintained ^[2][3][4].