Caffeine and Methylliberine: A Human Pharmacokinetic Interaction Study

Introduction: Methylliberine and theacrine are methylurates found in the leaves of various Coffea species and Camellia assamica var. kucha, respectively. We previously demonstrated that the methylxanthine caffeine increased theacrine’s oral bioavailability in humans. Methods:  Consequently, we conducted a double-blind, placebo-controlled pharmacokinetic study in humans administered methylliberine, theacrine, and caffeine to determine methylliberine’s pharmacokinetic interaction potential with either caffeine or theacrine. Subjects received an oral dose of either methylliberine, caffeine, methylliberine plus caffeine, or methylliberine plus theacrine using a randomized, double-blind, crossover design. Blood samples were analyzed using UPLC-MS/MS.    Results: Methylliberine exhibited linear pharmacokinetics that were unaffected by co-administration of either caffeine or theacrine. However, methylliberine co-administration resulted in decreased oral clearance (41.9 ± 19.5 vs. 17.1 ± 7.80 L/hr) and increased half-life (7.2 ± 5.6 versus 15 ± 5.8 hrs) of caffeine. Methylliberine had no impact on caffeine’s maximum concentration (440 ± 140 vs. 458 ± 93.5 ng/mL) or oral volume of distribution (351 ± 148 vs. 316 ± 76.4 L). Conclusions: We previously demonstrated theacrine bioavailability was enhanced by caffeine, however, caffeine pharmacokinetics were unaffected by theacrine. Herein, we found that methylliberine altered caffeine pharmacokinetics without a reciprocal interaction, which suggests caffeine may interact uniquely with different methylurates.