Effect of the Irregular Inner Shape of a Glass Vessel on Prednisone Dissolution Results

Introduction Dissolution testing has increased in value and significance over the last quarter century. It has been used extensively to guide formulation development and to monitor formulation development,formulation changes, and manufacturing of products for new drugs. It is also widely used as a quality control tool to monitor the batchto-batch consistency of drug release from a product. There are reports that dissolution testing involves a large number of variable factors and that obtaining reproducible results between apparatus,within laboratories,and between laboratories is difficult (1,2). The fact that significant withinand between-apparatus variability can exist for certain formulations,even though these apparatus meet the USP calibration criteria,has been reported (3). Recent research results have confirmed that dissolution testing is a highly variable technique such that test results for the same lot of USP calibrator tablets deviated from the acceptable USP range at 15 of 28 laboratories performing dissolution testing (4). In recent years,significant modifications and improvements have been made to the apparatus used in dissolution testing. Often overlooked is a critical technical issue that remains with regard to the glass vessel in the dissolution tester. A glass vessel is generally made from large–diameter glass tubing,and the bottom of the vessel is shaped by hand from the outside while the tubing is heated (5). Irregular interior surfaces result,and the curvature of the inner bottom varies from one vessel to the next,producing variation in dissolution test results (6,7). The vessels formed using such glass tubing are widely used in dissolution testing. A glass vessel with an almost ideal inner shape was recently developed using a new glass processing technology. This paper describes the effects of the irregular inner shape of a glass vessel on drug dissolution results. The shape of the inside of two conventional vessels,vessel A (manufacturer A,Japan) and vessel B (manufacturer B,USA),was measured using a three-dimensional coordinate measuring machine. The results were compared with those for a recently developed glass vessel (precision vessel). In addition,dissolution of USP Prednisone Calibrator tablets was compared using vessel A and the precision vessel.