Comparative bioavailability of two tablet formulations of diclofenac sodium in normal subjects

A comparative bioavailability study and in vitro characterization were conducted on two commercial products of diclofenac sodium (Voltaren "A" and Inflaban "B") in the form of enteric-coated tablets (25 and 50 mg). The two products were found similar in weight variation and content uniformity and both met the British Pharmacopeia requirements of disintegration for enteric-coated tablets. The dissolution in vitro revealed that product B was characterized by a faster rate compared to product A. The bioavailability of single doses, 2 x 50 and 2 x 25 mg, of each product was carried out respectively, on 14 and 6 normal male volunteers, according to a randomized complete block design. Blood samples were obtained over a 12-hour interval and serum concentrations of the drug were determined using an HPLC assay. The two products were found bioequivalent as assessed by AUC. However, the tmax value was found to be significantly smaller for product B compared to product A indicating that product B is apparently absorbed at a faster rate. Further, product B was characterized by higher Cmax values, although these were not statistically different from the corresponding values of product A. These findings are consistent with the in vitro dissolution pattern of the two products, and the differences in the rate of absorption may have therapeutic implications.