The increase in oral availability of felodipine and other commonly used medications when taken with grapefruit juice has been assumed to be due to inhibition of CYP3A4, a cytochrome P450 that is present in liver and intestine. To evaluate the effect of repeated grapefruit juice ingestion on CYP3A4 expression, 10 healthy men were given 8 oz of grapefruit juice three times a day for 6 d. Before a...

Previous studies indicate that blood levels of cyclosporin-A are increased by concomittant administration of grapefruit juice in healthy subjects and patients. It was suggested that grapefruit juice could inhibit the metabolism of cyclosporin-A by CYP3A4, the predominant cytochrome P450 enzyme in the gut wall and liver. However, up to date, the mechanism of action of grapefruit juice has not be...

action between grapefruit and certain medications more than 20 years ago. Currently, more than 85 drugs, most of which are available in Canada, are known or predicted to interact with grapefruit. This interaction en hances systemic drug concentration through impaired drug metabolism. Many of the drugs that interact with grapefruit are highly prescribed and are essential for the treatment of imp...

Grapefruit is a popular, tasty and nutritive fruit enjoyed globally. Biomedical evidence in the last 10 years has, however, shown that consumption of grapefruit or its juice is associated with drug interactions, which, in some cases, have been fatal. Grapefruit-induced drug interactions are unique in that the cytochrome P450 enzyme CYP3A4, which metabolises over 60% of commonly prescribed drugs...

29-year-old man, who had been taking a prescription allergy medication, twice a day, for over a year, drank two glasses of grapefruit juice with his medication and went out to mow the lawn. Suddenly, he became ill, stumbled into his home and collapsed. The coroner found that the man had died of irregular heartbeats caused by drug toxicity. Because of the deadly consequences of this allergy medi...

I glad to see James Maskalyk’s review of grapefruit and drug interactions, as I have been concerned for some time about the need to increase awareness of this issue. However, I would like to comment on drugs that were listed as if the effects were equal. Some patients enjoy grapefruit, and it is unkind to impose an unnecessary prohibition. The magnitude of the grapefruit effect is related to th...

The novel finding that grapefruit juice can markedly augment oral drug bioavailability was based on an unexpected observation from an interaction study between the dihydropyridine calcium channel antagonist, felodipine, and ethanol in which grapefruit juice was used to mask the taste of the ethanol. Subsequent investigations showed that grapefruit juice acted by reducing presystemic felodipine ...

BACKGROUND 6',7'-Dihydroxybergamottin is a furanocoumarin that inhibits CYP3A4 and is found in grapefruit juice and Seville orange juice. Grapefruit juice increases the oral bioavailability of many CYP3A4 substrates, including cyclosporine (INN, ciclosporin), but intestinal P-glycoprotein may be a more important determinant of cyclosporine availability. OBJECTIVES To evaluate the contribution...

Editorial Lown et al. (1) report a significant advance in describing a new mechanism by which ingested nutrients may change exposure to drug therapy. Grapefruit juice was reported to increase plasma concentrations of felodipine and nifedipine when the drug was concurrently administered with grapefruit juice (2). The potential clinical importance of such an interaction was noted when cyclosporin...

The reported effects of grapefruit (Citrus paradisi Macf.) juice on oral bioavailability of certain prescription drugs have led to the discovery of the inhibition by compounds in grapefruit of cytochrome P450 3A4 (CYP3A4) in the intestinal wall and liver. Recent evidence indicates that furanocoumarins related to bergamottin [5-[(3',7'-dimethyl-2',6'-octadienyl)oxy]psoralen] are primarily respon...