Introduction: Degree of skin penetration of topical drugs and cosmetics is a crucial point
concerning their effects and tolerability. For testing drug delivery across the dermal barrier different in
vitro and in vivo assays have been developed. Caffeine has been shown to have beneficial effects
against skin aging, sunburn and hair-loss, and it is protective against melanoma and non-melanoma
type skin cancers. Aim of our study was to set up an assay system to evaluate caffeine penetration from
topical formulation into the skin.
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Methods: Franz diffusion cells consisting of either a filter paper or an artificial membrane or rat skin
were used as in vitro/ex vivo test systems and transdermal microdialysis in anaesthetized rats was performed
as an in vivo assay.
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Results: Results indicate that Franz diffusion cell studies provide a good approximation of the release
of caffeine from the formulation but are not able to differentiate between 2% and 4% cream concentrations.
The maximum concentrations (Cmax) in case of the 2% cream formulation were 708.3 (2.7 μm
pore), 78.7 (0.8 µm pore), 45.3 (0.45 µm pore) and 44.9 (rat skin) µg/7.5 mL, respectively. The in vivo
microdialysis experiments were in accordance with the in vitro and ex vivo results and gave more information
on the dynamics and follicular and transcellular phases of drug penetration through the layers
of the skin.
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Discussion and Conclusion: Taken together, Franz diffusion cell and transdermal microdialysis are a
good combination to evaluate caffeine release and penetration into the skin from the formulations
tested. This system might also be used for rapid testing of other hydrophilic topical drugs and has a
benefit in the prediction for human skin absorption and tolerability studies, in an early phase of drug
development.
A rapid in vivo assay system for analyzing the organogenetic capacity of human kidney cells