The in vitro release of some antimuscarinic drugs from monoolein/water lyotropic liquid crystalline gels

Purpose. To investigate the potential use of a monoolein/water lyotropic liquid crystalline gel for the vaginal delivery of the antimuscarinic drugs, propantheline bromide and oxybutynin hydrochloride to treat urinary incontinence, using Myverol 18-99 as a commercially available grade of monoolein. Methods. The influence of propantheline bromide and oxybutynin hydrochloride on the phase structure of Myverol 18-99/water gels was investigated using polarising microscopy. The in-vitro release of the antimuscarinic drugs from Myverol 18-99/water gels was determined and the release pattern interpreted with the aid of results from swelling studies and partition coefficient determinations. Results. Myverol 18-99 forms gels with lyotropic liquid crystalline structures in the presence of water. The addition of propantheline bromide and oxybutynin hydrochloride promoted the formation of gels with a lamellar phase structure. The gels absorbed water at a rate inversely proportional to their initial water content until they reached an equilibrium water content of ~40% w/w whilst maintaining their physical integrity. The release of the antimuscarinic drugs was sustained over a period of ~18 hours and followed square root of time kinetics indicating that the rate of release was diffusion controlled. Conclusions. The in-vitro release behaviour of Myverol 18-99/water gels suggested that they are suitable carriers to deliver propantheline bromide or oxybutynin hydrochloride. The results of swelling studies indicated that a confined area, such as the vaginal cavity, would be a suitable site of administration.