Article date: November 2011
By: Xin Liu, Jeff E. Grice, Juergen Lademann, Nina Otberg, Sindy Trauer, Alexa Patzelt, Michael S. Roberts, in Volume 72, Issue 5, pages 768-774
WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT
• Depending on the body site and the substances, the hair follicles can contribute significantly to the penetration of topically applied substances. However, the quantitative and selective description of the follicular and intercellular penetration kinetics is difficult due to the lack of suitable models to differentiate between the different penetration pathways. Recently, for the first time, the follicular transport was measured directly in man in vivo indicating that the hair follicles are responsible for a fast delivery of topically applied substances.
WHAT THIS STUDY ADDS
• In the present study, pharmacokinetic principles were applied to define the underlying relative penetration of caffeine through follicles and through intact stratum corneum with time in vivo. Absorption from hair follicles was found to contribute more than one third of the total percutaneous absorption of caffeine. Additionally, it was observed that the uptake by the hair follicles appeared at early times and was transient.
AIMS The aim of this study was to define the underlying relative penetration of caffeine through hair follicles and through intact stratum corneum with time in vivo through pharmacokinetic modelling.
METHODS Caffeine plasma concentration–time profiles after topical application into skin with or without hair follicle blocking were modelled using the Wagner–Nelson method or a compartmental model with first order absorption and elimination. Pharmacokinetic parameters describing absorption rate and extent of absorption through hair follicles or the stratum corneum were determined separately and compared with each other.
RESULTS The obtained pharmacokinetic parameters from the two methods were similar. The absorption rate constant of caffeine for hair follicles was nearly 10 times higher than that for the stratum corneum and the percentage of absorption from hair follicles was more than half of that of the stratum corneum. In addition, the absorption from the stratum corneum showed an approximately 10 min delay while there was no delay for absorption from hair follicles. All caffeine absorbed by hair follicles occurs within 30 min of application and accounts for 10.5 to 33.8% of the total amount absorbed across the skin for all subjects, whereas absorption of caffeine through the stratum corneum can occur over several hours.
CONCLUSION Hair follicles contribute significantly to percutaneous absorption of caffeine after topical application in man in vivo only at times soon after application.
DOI: 10.1111/j.1365-2125.2011.04022.x
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