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Laboratory of Drug Disposition and Pharmacogenetics, Departments of Pharmaceutical Sciences (J.S.M.), Psychiatry and Behavioral Sciences (J.L.D., C.L.D., R.M.T., J.-S.W., Y.R.), and Surgery (K.D.C.), Medical University of South Carolina, Charleston, South Carolina
Green tea extract is a widely used dietary supplement. The objective of this study was to assess the influence of a decaffeinated green tea (DGT; Camellia sinensis) extract on the activity of the drug-metabolizing enzymes cytochrome P-450 2D6 and 3A4. Probe drugs dextromethorphan (30 mg, CYP2D6 activity) and alprazolam (ALPZ; 2 mg, CYP3A4 activity) were administered orally to healthy volunteers (n = 11) at baseline, and again after treatment with four DGT capsules/day for 14 days. Each DGT capsule contained 211 ± 25 mg of green tea catechins and <1 mg of caffeine. Dextromethorphan metabolic ratios (DMRs) and alprazolam pharmacokinetics were determined at baseline and after DGT treatment. There were no significant differences in ALPZ pharmacokinetics at baseline and after DGT treatment (all P values 
0.05; maximum concentration in plasma, 33 ± 8 versus 34 ± 13 ng/ml; time to reach maximum concentration in plasma, 1.4 ± 1.2 versus 1.4 ± 1.2 h; area under the plasma concentration versus time curve, 480 ± 119 versus 510 ± 107 h · ng · ml-1; half-life of elimination, 12.3 ± 1.7 versus 13.1 ± 3.4 h). The DMR was 0.053 ± 0.045 at baseline and 0.041 ± 0.032 after DGT supplementation (P > 0.05). The plasma concentration of the green tea flavonoid, (-)-epigallocatechin gallate, reached 1.3 ± 1.8 µM 2 h after DGT treatment. Our results indicate that DGT is unlikely to alter the disposition of medications primarily dependent on the CYP2D6 or CYP3A4 pathways of metabolism.
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