Evaluation of carboxymethyl guar films for the formulation of transdermal therapeutic systems

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.