Herb-Drug Interactions: Theory versus Practice
The goal of this special issue is to clarify some of the more confusing and controversial subjects within the area of herb-drug interactions. The concept that foods and botanical agents, officially classified as over-the-counter dietary supplements, could enhance or reduce the effects of prescribed medications has gained our attention only gradually. But with almost $5 billion in sales in the United States in 2007, herbal dietary supplements are now demanding our utmost attention [1]. The issue of food-drug interactions first became widely known in 1989 when grapefruit was first found to increase the blood levels of felodipine, a calcium channel blocker, and later, in 1996, terfenadine, a non-sedative antihistamine. Subsequent investigations suggested that these effects were due to inhibition of intestinal CYP3A4 and P-gp by naringenin and furanocoumarins, naturally-occurring substances in grapefruit. Terfinadine was removed from the market in 1998 because of its high rate of interactions; inhibition of CYP3A4 led to elevated blood levels, which caused prolonged QT intervals and subsequent cardiac arrhythmias.