Application of D-Optimal Mixture Design in the Development of Nanocarrier-Based Darifenacin Hydrobromide Gel

Background: Darifenacin hydrobromide, a BCS Class II drug, is poorly bioavailable due to extensive first-pass metabolism. The present study is an attempt to investigate an alternative route of drug delivery by developing a nanometric microemulsion-based transdermal gel for the management of an overactive bladder. Methods: Oil, surfactant, and cosurfactant were selected based on the solubility of the drug, and surfactant: cosurfactant in surfactant mixture (Smix) was selected at a 1:1 ratio as inferred from the pseudo ternary phase diagram. The D-optimal mixture design was used to optimize the o/w microemulsion wherein the globule size and zeta potential were selected as dependable variables. The prepared microemulsions were also characterized for various physico-chemical properties like transmittance, conductivity, and TEM. The optimized microemulsion was gelled using Carbopol 934 P and assessed for drug release in vitro and ex vivo, viscosity, spreadability, pH, etc. Results: Drug excipient compatibility studies showed that the drug was compatible with formulation components. The optimized microemulsion showed a globule size of less than 50 nm and a high zeta potential of -20.56 mV. The ME gel could sustain the drug release for 8 hours as reflected in in vitro and ex vivo skin permeation and retention studies. The accelerated stability study showed no significant change in applied storage conditions. Conclusion: An effective, stable, non-invasive microemulsion gel containing darifenacin hydrobromide was developed. The achieved merits could translate into increased bioavailability and dose reduction. Further confirmatory in vivo studies on this novel formulation, which is a cost-effective & industrially scalable option, can improve the pharmacoeconomics of overactive bladder management.