Comparison of Flow-Through Cell and Paddle Methods for Testing Vaginal Tablets Containing a Poorly Water-Soluble Drug

Purpose: To evaluate the usefulness of the flow-through cell apparatus for testing commercial vaginal tablets containing poorly water-soluble clotrimazole.
Methods: The effect of experimental conditions (type of dissolution medium, flow rate and positioning of the tablet) on the dissolution profile of clotrimazole were examined and optimal parameters for conducting the experiments were determined. The amount of drug released was analyzed by high performance chromatography (HPLC) at 210 nm. The usefulness of the flow-through cell apparatus was compared to FDA recommended paddle apparatus.
Results: Using acetate buffer pH 5.2 containing 1 % SDS, both methods gave different dissolution profiles. The paddle apparatus tended to give faster rate of dissolution (approx. 88.5 % during the first 20 min of the experiment), which was probably caused by higher agitation and greater surface area of the drug-dissolution medium in a vessel. In the flow-through cell method, total drug release was definitely slower and was observed after 2 to 5 h; at a flow rate of 16 ml/min, more than 80 % of the drug dissolved after 30 min of the test. It was noticed that raising the flow rate of the dissolution medium caused significantly higher drug release.
Conclusion: The results demonstrate that the flow-through cell method is reproducible and can be successfully used for evaluating in vitro dissolution of clotrimazole from non-modified release tablets. The slower rate of dissolution obtained in the flow-through cell method would help to distinguish between different formulations.

Keywords
Dissolution test, Flow-through cell method, Paddle method, Clotrimazole