Grapefruit juice (drug interactions)

Cyclosporin, terfenadine and most calcium channel blockers should not be taken with grapefruit juice. This is because grapefruit juice inhibits the metabolism of certain drugs by enzymes of subfamily cytochrome P45 (CYP 3A4 (2)). The effect reduces the metabolism of terfenadine, cyclosporin, and calicum channel blockers (other than amlodipine and diltiazem).

Statins and grapefruit juice

• simvastatin and grapefruit juice - pharmacokinetic evidence suggests that grapefruit juice should be avoided altogether, as even modest quantities of this drink can significantly increase exposure to simvastatin (3)
• for atorvastatin - patients should also avoid drinking large quantities of grapefruit juice (3)

Reference:

1. Current Problems in Pharmacovigilance (1997); 23:2.
2. Walter-Sack I, Klotz U (1996). Influence of diet and nutritional status on drug metabolism. Clin Pharmacokinetics, 31, 47-64.
3. Current Problems in Pharmacovigilance (2004); 30: 1-12.