Research: MARKOWITZ and colleagues,

Listed in Issue 53


MARKOWITZ and colleagues, Department of Pharmaceutical Sciences, Medical University of South Carolina, Charleston 29425 USA. studied the effects of St Johns wort (Hypericum perforatum) upon the activity of cytochrome P-450 (CYP) 2D6 and 3A4.



Probe substrates dextromethorphan (2D6 activity) and alprazolam (3A4 activity) were taken orally with and without the co-administration of St Johns wort in seven normal volunteers. Urinary concentrations of dextromethorphan and dextrorphan were quantified and dextromethorphan metabolic rations (DMRs) determined. Validated HPLC methods were used to quantify all compounds of interest.


No statistically significant differences were discovered in any estimated pharmacokinetic parameter for alprazolam or DMRs.


These results suggest that St Johns wort when taken at recommended doses for depression, is unlikely to inhibit CYP 2D6 or CYP 3A4 activity.


Markowitz JS et al. Effect of St Johns wort (Hypericum perforatum) on cytochrome P-450 2D6 and 3A4 activity in healthy volunteers. Life Sciences 66(9): PL133-9. 21 Jan 2000.

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