Published: Journal of Analytical Toxicology, Volume 22, Number 7, November/December 1998, pp. 596-600
Caffeine Demethylation Monitoring Using a Transdermal Sweat
Patch
Tom Delahunty and Don Schoendorfer
Caffeine and two metabolites (paraxanthine and theobromine) were quantitated
by high-performance liquid chromatography (HPLC) using extracts from transdermal
sweat patches that continously collected and stored analytes lost through the
skin. Following caffeine consumption, remarkably clean chromatograms were obtained
with minimal sample preparation. Caffeine and paraxanthine accumulated in the
patch at comparable rates, and theobromine accumulated more slowly. A major
urinary metabolite, 1-methylxanthine, was notably absent in sweat-patch and
plasma extracts, a finding which favors a renal source for this metabolite.
A simple, noninvasive approximation of N-demethylation can be made by
calculating the paraxanthine/ caffeine and theobromine/caffeine ratios in the
patch extract. These ratios were significantly reduced in high-dose (600 mg)
versus low-dose (200 mg) subjects, possibly reflecting a decreased clearance
of caffeine. Because the sweat patches can be worn for several days, the technique
gives a multiday historical record which reflects the fluctuating systemic concentration
of caffeine and its hepatic metabolites and thus might be useful to noninvasively
monitor compliance by caffeine-restricted patients or to assess drug-metabolizing
status.
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