COMPARATIVE BIOAVAILABILITY AND PHYSICOCHEMICAL QUALITY ASSESSMENT OF INNOVATOR AND GENERIC BRANDS OF DICLOFENAC AND PARACETAMOL IN NIGERIA

Abstract

Abstract 
Background: Substandard and falsified analgesics remain a major public health threat in low- and middle-income countries. This study evaluated the physicochemical quality and relative bioavailability of widely used innovator and generic brands of diclofenac (50 mg) and paracetamol (500 mg) marketed in Nigeria. Methods: Six brands (three diclofenac, three paracetamol) were subjected to pharmacopoeial tests (weight uniformity, hardness, friability, disintegration, dissolution, and assay). A randomized, open-label, single-dose, three-period crossover bioavailability study was conducted in 33 healthy volunteers with a 7-day washout. 
Plasma concentrations were quantified by validated UV-spectrophotometry. Bioequivalence was concluded if the 90% confidence interval (CI) for Cmax and AUC₀₋ₜ fell within 80.00-125.00%. Results: Two generic paracetamol brands (Brand P and Brand E) failed assay (<70% labelled content). One generic diclofenac (Brand G) showed markedly reduced exposure (Cmax ratio 76%, AUC ratio 67%). Brand C (diclofenac) and all paracetamol brands that passed quality control were bioequivalent to their respective innovators. Conclusion: While some generics are bioequivalent and interchangeable, others are substandard and pose clinical risks. Strengthened post-market surveillance and routine bioavailability testing are urgently needed in Nigeria.