Polyelectrolyte Gels as Drug Carriers I: Poly (Methyl Methacrylate-co-Potassium Acrylate) Beads

Abstract

Reported herein is an indirect process to synthesize highly swellable anionic gel beads based on poly(methyl methacrylate-co-potassium acrylate) (PMMA/A-K), which is highly swellable in weak acid. The Release of labetalol HC1 (solubility in water 1g/60 ml) from PMMA/A-K beads was not affected by buffer concentrations above 1/15 M. However, as the buffer concentration was decreased from 1/15 M to 0.01 M, the release rate decreased. Release kinetics are close to zero-order with an exponent of n = 0.904 in 0.01 M buffer concentration, whereas the exponent n in 0.2 M and 1 /15 M is 0.635 and 0.768, respectively. With a 0.01 M buffer concentration, n ranges from 0.876 to 0.933 as pH changes from 9.0 to 6.8, indicating that the release kinetics maintain a zero-order irrespective of the pH's examined in this study. This zero-order kinetics at 0.01 M results from large dimensional changes of about D_f/D_i = 2.35 to 2.63. The degree of swelling during drug release contribute to the increase in the diffusion coefficient of the drug in the swollen matrix, which in turn can lead to zero-order kinetics.