Eudragit-based transdermal delivery system of pentazocine: Physico-chemical, in vitro and in vivo evaluations

The present study was aimed to develop a matrix-type transdermal formulation of pentazocine using mixed polymeric grades of Eudragit RL/RS. The possible interaction between drug and polymer used were characterized by FTIR, DSC and X-RD. X-RD study indicates a change of state of drug from crystalline to amorphous in the matrix films prepared. The matrix transdermal films of pentazocine were evaluated for physical parameters and in vitro dissolution characteristic using Cygnus' sandwich patch holder. Irrespective of the grades of Eudragit polymer used, the thickness and weight per patch were similar. In vitro dissolution study revealed that, with an increase in the proportion of Eudragit RS (slightly permeable) type polymer, dissolution half life (t(50%)) increases and dissolution rate constant value decreases. Selected formulations were chosen for these pharmacokinetic studies in healthy rabbits. The relevance of difference in the in vitro dissolution rate profile and pharmacokinetic parameters (C(max), t(max), AUC((s)), t(1/2,) K(el), and MRT) were evaluated statistically. In vitro dissolution profiles (DRC and t(50%)) and pharmacokinetic parameters showed a significant difference between test products (P<0.01). Quantitatively good correlation was found between the percentage of drug absorbed from the transdermal patches and AUC((s)).