RESUMO
Carboxymethyl guar (CMGS), an anionic semisynthetic guar gum derivative was evaluated for its suitability of use in transdermal drug-delivery systems. Terbutaline sulfate (TS) was used as a model drug. The diffusion of terbutaline sulfate from CMGS solution was relatively slower at pH 5 than at pH 10. It is most likely that the interaction between CMGS and terbutaline sulfate at pH 5 is physical, involving static interaction. The ability of such interactions in modifying the release kinetics of drug from the CMGS transdermal films was studied. The release was exponential from pH 5 formulations whereas the release rate followed zero or Higuchian order from pH 10 formulations. However, the diffusion kinetics of both pH 5 and pH 10 formulations followed zero order across human cadaver epidermis. Such an interaction was also found to alter the pharmacokinetic parameters of the drug. The steady-state concentration of TS was relatively consistent and the bioavailability was approximately 50% higher in pH 5 formulations than pH 10. The elimination rate constant/half-life was significantly different between pH 5 and pH 10 formulations.