Chapter 6 - Drug–herb and drug–food interactions and effects on therapeutic drug monitoring

Abstract

Herbal supplements are sold under the dietary supplement act of 1994 and do not require FDA approval. Although general public consider herbal supplements are safe and effective, toxicity and even fatality may occur from use of certain herbal supplements such as kava. In addition, several herbal supplements show clinically significant interactions with specific drugs. St. John’s wort, an herbal antidepressant interacts with many drugs both pharmacokinetically and pharmacodynamically. Pharmacokinetic interactions of St. John’s wort with many drugs including cyclosporine, tacrolimus, warfarin, and digoxin may cause treatment failure due to increased clearances of these drugs. Certain herbal supplements reduce efficacy of warfarin while other herbal supplements such as garlic supplement may increase efficacy of warfarin. Therapeutic drug monitoring of cyclosporine and tacrolimus or INR monitoring during warfarin therapy can identify such clinically significant drug–herb interactions.