HERBAL MEDICINALS - SELECTED CLINICAL CONSIDERATIONS FOCUSING ON KNOWN OR POTENTIAL DRUG-HERB INTERACTIONS

Herbal medicinals are being used by an increasing number of patients w ho typically do not advise their clinicians of concomitant use. Known or potential drug-herb interactions exist and should be screened for. If used beyond 8 weeks, Echinacea could cause hepatotoxicity and there fore should not be used with other known hepatoxic drugs, such as anab olic steroids, amiodarone, methotrexate, and ketoconazole. However, Ec hinacea lacks the 1,2 saturated necrine ring associated with hepatoxic ity of pyrrolizidine alkaloids. Nonsteroidal anti-inflammatory drugs m ay negate the usefulness of feverfew in the treatment of migraine head aches. Feverfew, garlic, Ginkgo, ginger, and ginseng may alter bleedin g time and should not be used concomitantly with warfarin sodium. Addi tionally, ginseng may cause headache, tremulousness, and manic episode s in patients treated with phenelzine sulfate. Ginseng should also not be used with estrogens or corticosteroids because of possible additiv e effects. Since the mechanism of action of St John wort is uncertain, concomitant use with monoamine oxidase inhibitors and selective serot onin reuptake inhibitors is ill advised. Valerian should not be used c oncomitantly with barbiturates because excessive sedation may occur. K yushin, licorice, plantain, uzara root, hawthorn, and ginseng may inte rfere with either digoxin pharmacodynamically or with digoxin monitori ng. Evening primrose oil and borage should not be used with anticonvul sants because they may lower the seizure threshold. Shankapulshpi, an Ayurvedic preparation, may decrease phenytoin levels as well as dimini sh drug efficacy. Kava when used with alprazolam has resulted in coma. Immunostimulants (eg, Echinacea and zinc) should not be given with im munosuppressants (eg, corticosteroids and cyclosporine). Tannic acids present in some herbs (eg, St John wort and saw palmetto) may inhibit the absorption of iron. Kelp as a source of iodine may interfere with thyroid replacement therapies. Licorice can offset the pharmacological effect of spironolactone. Numerous herbs (eg, karela and ginseng) may affect blood glucose levels and should not be used in patients with d iabetes mellitus.