Interaction between Grapefruit Juice and Drugs*

There is a possibility that even a glass of grapefruit juice (GFJ) taken several hours before oral medication may enhance the bioavailability of many drugs, exaggerate the drug action, and increase the toxic effect by exaggerating the potency of the drug. This can be explained by inhibition of CYP3A4 in the small intestine by GFJ, thus suppressing drug metabolism. This interaction with GFJ is likely to occur mainly with those drugs that are metabolized by CYP3A4 and are associated with low bioavailability when given via an oral route. Thorough instruction on medication is necessary when these drugs are administered to patients. Examples of these drugs include: dihydropyridine calcium antagonists, terfenadine, cyclosporine, and carbamazepine.