Herb-drug Interactions
by Paul Bergner
Interactions
between medicinal herbs and drugs is a topic that is poorly studied in the scientific
literature. It is a major concern for the clinical herbalist, however, especially
for elder patients, who are likely to be taking multiple prescription drugs. Here
are a few recent reports of possible drug-herb interactions
Kava and Xanax
Kava (Piper methysticum<D>) has gained recent popularity in North America
due to its relaxing effects, both as a recreational herb and as a treatment for
anxiety (See MH<D> Vol 8, No 1). European research has shown that it may
make an effective substitute for members of the benzodiazepine class of anti-anxiety
drugs, which includes Valium. A recent case report, however, suggests caution
before using kava along with<D> benzodiazepine drugs. A patient apparently
lapsed into a "semicomatous state" due to an interaction between kava
and the drug alprazolam (Xanax) (Almeida and Grimsley). The benzodiazepines generally
lose effect within 8-12 hours, but secondary metabolites capable of interacting
with other substances linger in the blood for 24 or more hours afterwards. Interactions
between alcohol and the benzodiazepine drugs are well-known - alcohol potentiates
their effects - but herbal interactions have not been studied or previously recorded.
Ginkgo
and blood thinners
Interactions between blood-thinning herbs and pharmaceutical
medications with the same action present perhaps the greatest risk of drug-herb
interactions in modern practice. The risk is due to the gravity of the underlying
condition that requires a blood-thinner, and to the fragile dose range and serious
side effects of of the pharmaceutical drugs themselves. The drugs must be given
in high enough doses to prevent the formation of life-threatening clots, but can
cause serious and life-threatening bleeding disorders if given in too high a dose.
A blood thinning herb can act like "the straw that broke the camel's back"
by thinning the blood enough to allow the drug to provoke a serious bleeding disorder.
The risk is probably greatest with heparin, warfarin, and coumarin derivatives,
but recent anecdotes indicate that interactions may also occur between blood thinning
herbs and such mild pharmaceutical blood-thinners as aspirin. Gingko biloba extract
(GBE) is a popular phytopharmaceutical in Europe, where it is a prescription medicine,
and in the U.S., where it is available in health food stores. A recent case report
in the New England Journal of Medicine<D> describes a case of spontaneous
bleeding into the eye from the iris within a week of onset of daily GBE supplementation
in a patient who had been taking aspirin to prevent a heart attack. GBE constituents
have demonstrated blood thinning activity (Kleinjen) and a previous case report
showed that it may cause bleeding disorders in a healthy patient even in the absence
of anticoagulant medication (Rowan and Lewis). I have also received case reports
from two practitioners about retinal hemorrhage in patients taking ginkgo without
other drugs, and one case of clotting problems during kidney dialysis (recurring
with rechallenge). In the current case, a 70-year old male had been taking aspirin
(one 325 mg tablet daily) for three years following coronary bypass surgery. He
began taking two 40mg tablets of GBE (50:1 extract), and one week later exhibited
blurred vision with a red streak visible inside the eye. The patient had no previous
history of eye disorders or recent eye trauma. The patient stopped taking the
GBE, but continued to take the aspirin. No bleeding recurred over a three month
follow-up period.
Chinese red sage
A case report of potentiation of the
effects of warfarin by the Chinese herb dan-shen (Salvia miltiorrhiza) <D>recently
appeared. Dan-shen is considered to enter the heart and pericardium channels and
is primarily used as a cardiovascular herb in China. In traditional Chinese medical
terms it invigorates blood circulation and nourishes the blood, among other activities.
The article reports a case of danshen-induced severe and dangerous abnormalities
of clotting in a patient with rheumatic heart disease taking warfarin simultaneously.
References
Almeida
JC, Grimsley EW. Coma from the health food store: interaction between kava and
alprazolam. Ann Intern Med. 1996 Dec 1;125(11):940-941
Kleijnen J, Knipschild
P. Ginkgo biloba. Lancet 1992;340:1136-9.
Rosenblatt M, and Mindel J. Spontaneous
Hyphema Associated with Ingestion of Ginkgo biloba Extract NEJM (1997)336;15:1108
Rowin
J, Lewis SL. Spontaneous bilateral subdural hematomas associated with chronic
Ginkgo biloba ingestion. Neurology 1996;46:1775-6.
Yu CM, Chan JC, Sanderson
JE. Chinese herbs and warfarin potentiation by 'danshen'. J Intern Med 1997 Apr;
241(4):337-339
Copyright 1997 by Paul Bergner. All right reserved