Post-Marketing Quality Evaluation and in Vitro Dissolution Kinetics of Multi-Source Diclofenac Potassium 50 Mg Tablets Marketed in Sudan: Implications for Therapeutic Interchangeability

Abstract Background Expansion of multi-source generic medicines has improved access to essential drugs but requires robust post-marketing surveillance to ensure therapeutic interchangeability, particularly in tropical climates. Diclofenac potassium, an immediate-release non-steroidal anti-inflammatory drug, relies on rapid dissolution for prompt analgesic action. This study evaluated the physicochemical quality, drug content, and in vitro dissolution characteristics of five commercial diclofenac potassium (50 mg) tablet brands marketed in Khartoum, Sudan. Methods In this comparative cross-sectional study, one innovator (Brand A) and four generic brands (Brands B–E) were evaluated according to United States Pharmacopeia (USP) specifications for weight variation, crushing strength, friability, disintegration time, assay, and dissolution. Dissolution profiles were generated over 60 minutes in pH 6.8 phosphate buffer and assessed using dissolution efficiency, similarity factor (f₂), and kinetic modeling. Results All brands complied with pharmacopeial specifications for weight variation, friability, disintegration time, and assay. However, multi-point dissolution testing identified clinically relevant differences not detected by single-point testing. Local Brand E failed the 30-minute dissolution criterion (76.6 ± 1.4%) and exhibited a dissimilar release profile (f₂ = 46.3), indicating delayed drug release. Local Brand D met the pharmacopeial requirement but showed an excessively rapid release profile (f₂ = 42.1), suggesting formulation-related dose-dumping risk. Imported generics (Brands B and C) demonstrated acceptable similarity to the innovator (f₂ ≥ 50). All brands followed first-order release kinetics (R² > 0.99), while Weibull shape parameters confirmed formulation-dependent release differences. Conclusions Although all brands met basic pharmacopeial quality standards, dissolution profile comparison and kinetic modeling revealed significant differences in release behaviour. Incorporating these approaches into routine post-marketing surveillance would strengthen regulatory decisions regarding generic substitution and therapeutic interchangeability.