The kinetics of isothermal nicotinamide release from poly(acrylic-co-methacrylic acid) loaded xerogel

Abstract

The isothermal kinetics of in vitro nicotinamide release from poly(acrylic-co-methacrylic acid) loaded xerogel into water was evaluated. The isothermal kinetics curves of nicotinamide release from poly(acrylic-co-methacrylic acid) xerogel were measured at different temperatures ranging from 296 K to 315 K. It was proven that the kinetics of nicotinamide release from poly(acrylic-comethacrylic acid) xerogel was a kinetically complex process which was neither controlled by the processes of drug diffusion nor with the relaxation of the xerogel. The kinetic of nicotinamide release from poly(acrylic-co-methacrylic acid) may be described by the kinetics model of reversible first order chemical reaction and the apparent activation energy have value of Ea,M5=14.1 kJ mol-1 and preexponential factor ln(AM min-1)=2.3. The rate constants of nicotinamide release (kR) and the rate constants of its reversible absorption reaction (kA) were calculated and found to fall within the range 0.019 min-1-0.033 min21 for kR and 0.014 min-1-0.016 min-1 for kA. The value of activation energy for the nicotinamide releas, Ea.R =21.25 kJ mol-1, is significantly higher than the value for the process of nicotinamide absorption (Ea,A=2.6 kJ mol-1). The rate of nicotinamide release was predetermined with the rate of nicotinamide molecules distribution between the hydrogel and surrounding solution.