Effect of silica and poly(ethylene glycol) on the in vitro release rate of2-pyridine aldoxime chloride from polysiloxane matrices

The release rate of 2-pyridine aldoxime chloride (PAM-Cl) from polysiloxane matrices was found to be in the order poly(vinylmethyldiethylsiloxane) (P( VM-DE)S) > poly(dimethyldiethyl siloxane) P(DM-DE)S > poly(vinylmethylsilox ane) (PVMS) > poly(dimethylvinylmethylsiloxane) (P(DM-VM)S) > poly(dimethyl siloxane) (PDMS). The time for 80% PAM-Cl release from polysiloxane matrice s was found to be in the range 5-14 h. Incorporation of silica (5-10%) as a filler in these matrices reduced the release of PAM-Cl and in some cases s topped drug release completely. However, the incorporation of crosslinked p oly(ethylene glycol) (PEG) (5-20%) in polysiloxane matrices increased the r elease rate and reduced the time for 80% drug release. Slow release formula tions were made by incorporating 5% silica and 5-20% PEG in PDMS, keeping t he PAM-Cl and PEG ratio 1:1. The formulations PDMS + 5% silica + 5-20% PEG + 5-20% PAM-Cl gave a slow release of PAM-Cl and the time for 80% drug rele ase was found to be 12 h in each case at pH 7.4 and 37 degrees C. PVMS and siloxane copolymers showed times for 80% drug release of 6-10 h in comparis on with 12 h for PDMS. Diffusion coefficient values for PAM-Cl-PDMS system are also calculated. (C) 2000 Society of Chemical Industry.