Transdermal Evaluation of Caffeine in Different Formulations and Excipients

Background: The stratum corneum (SC) forms a difficult physical barrier for drugs to pass through the skin. Several strategies were developed to overcome this barrier. Optimization of topical drug formulations by selected excipients may facilitate the penetration of drugs through the SC into the viable skin cells and ultimately into the systemic circulation. Methods: Here, both the influence of two formulations (a classic carbomer-based gel and a novel Pluronic lecithin organo gel (PLO gel)) and selected excipients (ethanol, propylene glycol, diethylene glycol monoethyl ether, isopropyl myristate (IPM), and water) with or without the penetration enhancer miconazole nitrate on the transdermal penetration characteristics of caffeine were determined using an in vitro Franz diffusion cell setup. Results: Higher fluxes were observed for the carbomer-based gel compared to the PLO gel. Among the commonly used excipients, IPM showed the best penetration enhancing properties, while the presence of the penetration enhancer miconazole nitrate did not significantly alter the apparent skin permeation characteristics for caffeine. Conclusion: The high ethanol percentage in the carbomer-based gel could explain the results as supported by our excipient data. Moreover, IPM could play a beneficial role in topical formulations as this excipient was responsible for a significant increase in the amount of caffeine penetrated through the skin. No overall statistical significant effect of the presence of miconazole nitrate as a penetration enhancer was observed.