Anticoagulation effects of warfarin reduced by taking ginseng
Further data have been reported on a ginseng/ warfarin interaction and problems combining St John's wort with conventional medicines.
A reduction in warfarin’s anticoagulant effect with American ginseng
is seen in a new trial from Chicago. Researchers randomised 20 volunteers
to take warfarin and either American ginseng or placebo. All subjects
received warfarin 5mg daily for three days in week 1 and in week 4. Beginning
in week 2, 12 subjects took powdered ginseng in capsules and the other
eight received placebo.
After two weeks of ginseng administration the peak international normalised
ratio (INR) decreased compared with placebo, a reduction of 0.19 (P=0.0012).
The INR area under the curve, peak plasma warfarin level and warfarin
AUC were also significantly reduced.
The authors note that ginseng alone appears to have the conflicting action
of promoting bleeding and delaying clot formation. They suggest that
ginseng contains substances which enhance the hepatic enzymes that break
down warfarin.
They say that, when considering warfarin treatment, prescribers should
ask patients about ginseng use (Annals of Internal Medicine 2004;141:23).
A systematic review of trials of St John’s wort interactions, reminds
clinicians and patients of possible decreases in bioavailablity with
conventional drugs taken with this herb. However, the review uncovers
problems with several published pharmacokinetic studies and the authors
call for better trials to guide clinical practice (BMJ 2004;329:27). |
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