Dissolution testing is useful for controlling the quality of oral products and rejecting bioinequivalent products. However, several sources of variability in dissolution tests can affect evaluations of quality. The purpose of this study was to investigate the effects of paddle-shaft position on the dissolution rates of a brand-name (BR) and four generic-equivalent (GE), rapid-release tablets of sodium diclofenac. The paddle was shifted 5 mm from the center of the vessel, and the dissolution profiles were compared with that obtained at the central position. Although the GEs had a wide range of variability and significantly different dissolution profiles, they were estimated to be equivalent to the BR when the paddle was set at the center of the vessel. The 5-mm-shifted position significantly increased the dissolution rates Of all products with the result that some GEs did not meet the criteria for equivalence.
In conclusion, paddle position is potentially a cause of error in GE equivalence assessments. The paddle should be accurately positioned at the center of the vessel in dissolution tests for the equivalence assessment of GEs.