Posted by: Hourglass PJ23 JUN 2011
Grapefruit juice is well known to affect the metabolism of several drugs, including felodipine and other dihydropyridine calcium channel blockers, buspirone, ciclosporin, simvastatin and atorvastatin. It has the potential to increase blood levels of these drugs by inhibiting the intestinal cytochrome-P450 enzyme CYP3A4 and the intestinal drug efflux pump P-glycoprotein.
Another way in which fruit juices alter bioavailability of oral drugs has now been identified. According to a review in the British Journal of Pharmacology (November 2010) the discovery was based on an unexpected finding when assessing the possibility of grapefruit juice increasing oral fexofenadine bioavailability. In follow-up studies, grapefruit or orange juice at low concentrations inhibited a drug uptake transporter, organic anion-transporting polypeptide OATP1A2, while high volumes of juice dramatically depressed oral fexofenadine bioavailability.
Grapefruit juice has been found to lower the bioavailability of several oral drugs transported by OATP1A2 (eg, fexofenadine, acebutolol, celiprolol, l-thyroxine), while orange juice has the same effect on others (atenolol, celiprolol, ciprofloxacin) as well as fexofenadine. Naringin, a flavonoid in grapefruit juice, seems to be a major causal component. This suggests that other vegetable and fruit juices might have the same effect. The inhibitory effect appears to last between two and four hours, so that the interaction might be avoided with appropriate intervals between drug administration and juice consumption.