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Received for publication April 6, 2004.
Revised May 26, 2004.
Accepted for publication May 26, 2004.
Green tea extract is a widely used dietary supplement. The objective of this study was to assess the influence of a decaffeinated green tea extract (DGT; Camellia sinensis) on the activity of the drug metabolizing enzymes cytochrome P-450 (CYP) 2D6 and 3A4. Probe drugs dextromethorphan (DM, 30mg, CYP2D6 activity) and alprazolam (ALPZ, 2mg, CYP3A4 activity) were administered orally to healthy volunteers (n =11) at baseline, and again following treatment with 4 DGT capsules/d for 14 d. Each DGT capsule contained 211±25 mg green tea catechins and <1 mg 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 (EGCG), reached 1.3 ± 1.8 µmol/L 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.
Key words:
CYP2D, CYP3A, cytochrome P450, drug interactions, human CYP enzymes, pharmacokinetics
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