Antifungal activity of econazole nitrate/cyclodextrin complex: Effect of pH and formation of complex aggregates

Econazole nitrate (ECN) is a weakly basic drug with very low aqueous solubility that hampers its permeation through biological membranes and results in low ECN bioavailability. Formation of drug/cyclodextrin (drug/CD) inclusion complexes is a formulation technology that can be applied to enhance drug solubility in aqueous media. The aim of this study was to determine the effect of CD complexation and pH adjustments on the ECN solubility. The ECN pH-solubility and ECN/CD phase-solubility profiles were determined. The solubility of ECN in aqueous acidic solutions containing α-cyclodextrin (αCD) was relatively high and much higher than in aqueous γ-cyclodextrin (γCD) solutions under same conditions. The complexation efficiency of the ECN/CD complex was relatively low for the unionized drug. Formation of ECN/CD inclusion complex was verified by proton nuclear magnetic resonance spectroscopy. Formation of ECN/CD complexes enhanced the drug stability during autoclaving. γCD complexes self-assembled to form nano- and microparticles whereas αCD complexes had negligible tendency to self-assemble. Formation of CD complex nano- and microparticles was investigated by dynamic light scattering and by drug permeation through semipermeable membranes of different molecular weight cut-off. The largest aggregate fraction was observed for the unionized ECN in aqueous pH 7.5 solution containing high CD concentration, that is 10% (w/v) CD. It was shown that in acidic solutions ECN/αCD can enhance the antifungal activity to filamentous fungi. This was associated with the increased ECN solubility and increase of readily available ECN molecules in aqueous αCD solutions.