Percutaneous release of caffeine from microemulsion, emulsion and gel dosage forms.

The transport of caffeine to the hypodermis by an alcohol-free o/w microemulsion was investigated and compared with an aqueous gel and an o/w emulsion. The microemulsion was well characterized and in vitro diffusion measurements through pig skin having the hypodermis either kept or removed were performed in static Franz cells. The microemulsion allowed delivery of a large fraction of the caffeine in the hypodermis: 23% of caffeine reached the hypodermis after 24h diffusion, 1.3-fold larger than from the emulsion and gel dosage forms. Half this amount was stored in the hypodermis, the other half continuing its diffusion to the receptor compartment of the Franz cell.