Positive Health Online

Abstract

GURLEY and colleagues, Department of Pharmaceutical Sciences, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA, have examined the effect of milk thistle and black cohosh on the metabolism of a major heart medicine, digoxin.

Background

The aim of this study was to test the hypothesis that phytochemical-mediated modulation of P-glycoprotein and other drug transport proteins may underlie many herb-drug interactions.

Methodology

16 healthy volunteers were randomly assigned to receive a standardized milk thistle (900 mg daily) or black cohosh (40 mg daily) supplement for 14 days, followed by a 30-day washout period. Subjects were also randomized to receive rifampin (600 mg daily, 7 days) and clarithromycin (1000 mg daily, 7 days) as positive controls for P-glycoprotein induction and inhibition, respectively. Digoxin was administered orally before and at the end of each supplementation and control period. Serial serum concentration-time profiles of digoxin were used to determine whether supplementation with milk thistle or black cohosh modified P-glycoprotein activity in vivo.

Results

No statistically significant effects on digoxin pharmacokinetics were observed following supplementation with either milk thistle or black cohosh. When compared with rifampin and clarithromycin, supplementation with these specific formulations of milk thistle or black cohosh did not appear to affect digoxin pharmacokinetics.

Conclusion

These supplements are not potent modulators of P-glycoprotein in vivo.

References

Gurley BJ, Barone GW, Williams DK, Carrier J, Breen P, Yates CR, Song PF, Hubbard MA, Tong Y, Cheboyina S. Effect of milk thistle (Silybum marianum) and black cohosh (Cimicifuga racemosa) supplementation on digoxin pharmacokinetics in humans. Drug Metabolism & Disposition 34 (1): 69-74, Jan 2006.