Formulation and Pharmacokinetic Evaluation of Controlled-Release Oxybutynin Tablets in Dogs

Purpose: To develop and optimize controlled-release (CR) oxybutynin chloride matrix tablets. Methods: Oxybutynin CR tablets were prepared by embedding drug-containing granules into a hydrogel matrix of hydroxypropyl methylcellulose (HPMC). A coating layer was then applied with a mixture of HPMC, ethylcellulose, shellac, and HPMC phthalate. The effect of several formulation variables on in vitro drug release was studied; furthermore, the drug release kinetics of the optimized formulation was evaluated. The in vivo pharmacokinetics of the optimized formulation was compared with those of commercial immediate-release and CR tablets in dogs. Results: The core tablets exhibited extended release consisting of drug release from the embedded granules through the erodible hydrogel matrix. Release rate was controlled by the amounts of swellingcontrol agent and hydrogel used. The optimized formulation followed zero-order release up to 24 h after an initial lag time. Maximum plasma drug concentration for the optimized and commercial CR tablets was 5.90 ± 1.42 and 6.47 ± 3.73 ng/mL, respectively, while the area under the plasma concentration– time curve was 101.40 ± 51.41 and 112.68 ± 65.89 ng∙h/mL, respectively. Conclusion: The formulated oxybutynin CR tablets exhibit prolonged drug release, thus rendering it a potentially suitable once-daily oral formulation for improved patient compliance.