HDCN Article Review/Hyperlink

Pisarik P

Grapefruit juice increases antihypertensive effect of calcium channel blockers

Arch Fam Med (Jul) 5:413-416 1996

Grapefruit juice appears to cause a significant range of drug interactions. In March of last year (Clin Pharmacol Therap 57:318-324, 1995) Hollander et al found that a small glass of grapefruit juice given every 3 hours for 3 hours caused substantial increase (by 185 ng/ml) in the peak concentration of cyclosporin. The postulated mechanism was inhibition of cyclosporin metabolism via cytochrome P450 enzymes in the gut wall and liver.

In the present paper, Pisarik reports an augmented anti-hypertensive effect of a patient taking a calcium channel blocker in a single patient. He cites other studies in which bioavailability of several calcium channel blockers appeared to be markedly increased by grapefruit juice. In this case, the mechanism appears to be due to the presence of flavonoids in grapefruit juice, which may inhibit metabolism of certain calcium channel blockers.

Comment: The scope of drug interactions due to grapefruit juice may be quite large and certainly deserves further study. (John T. Daugirdas, M.D., University of Illinois at Chicago)