A study on the relative bioavailability of a sustained-release formulation of diclofenac sodium

The bioavailability of an in vitro sustained-release formulation of diclofenac sodium was compared with a conventional product in six healthy male volunteers. The administration of a single dose (100 mg) of either formulation in a crossover design revealed significant differences in the extent of absorption as assessed by AUC. The relative bioavailability of the sustained-release formulation was found to be 53% compared with the conventional product. The Cmax for the sustained release formulation (0.54 +/- 0.29 micrograms ml-1) was significantly much lower than the corresponding value for the conventional formulation (4.12 +/- 0.91). However, the tmax for the sustained release formulation (3.6 +/- 2.1 h) was not significantly different from the corresponding value for the conventional formulation (2.5 +/- 0.4 h). Although the sustained release formulation showed serum concentration-time profiles characteristic of sustained products in vivo, it failed to attain therapeutic drug levels. The in vivo results were found inconsistent with the in vitro availability of the drug.