Formulation studies of microemulsions for topical applications of acyclovir

Microemulsions prepared using 1-decanol, oleic acid or oleyl alcohol as oils, Transcutol and 1,2- hexanediol as surfactant mixture and phosphate buffer pH 6.0 as aqueous phase were studied to verify the effect of the oils on pig-skin permeation and accumulation of acyclovir (ACV). Pseudoternary phase diagrams were constructed in the absence and in the presence of ACV. ACV-containing microemulsions had a restricted area of existence compared to those without the drug. A cationic charge-inducing agent, L-alanine benzyl ester, was added to the formulations to prepare positively-charged microemulsions. Full-thickness pig ear skin was used for ACV permeation experiments using positively- and negatively-charged microemulsions and a control suspension. The presence of oleyl alcohol or oleic acid increased the flux but not the drug skin accumulation compared to a control suspension, while the use of the cationic charge-inducing agent had no influence on the formulation performance. A two-fold increase in ACV accumulation was found using the microemulsions containing 1-decanol, maintaining intact the structure of the stratum corneum, as demonstrated by the DSC analysis. Microemulsions containing 1-decanol could significantly optimize drug targeting, maintaining the structure of the stratum corneum intact.