Grapefruit juice

Sliced pink grapefruit

Grapefruit juice is the fruit juice from grapefruits. It is rich in Vitamin C and ranges from sweet-tart to very sour. Variations include white grapefruit, pink grapefruit and ruby red grapefruit juice.^[1][2]

Drug interactions

Grapefruit juice, and grapefruit in general, is a potent inhibitor of the intestinal cytochrome P450 enzyme CYP3A4, which can impact the metabolism of a variety of drugs, increasing their bioavailability when administered orally.^{[3][4][5][6][7]} In some cases, this can lead to a fatal interaction with drugs like astemizole or terfenadine.^[4] The effect of grapefruit juice with regard to drug absorption was originally discovered in 1989. However, the effect became well-publicized after being responsible for a number of deaths due to overdosing on medication.^[8] However, the first published report on grapefruit drug interactions was in 1991 in the Lancet (British) entitled "Interactions of Citrus Juices with Felodipine and Nifedipine." and was the first reported food-drug interaction clinically.

Recently some researchers have shown that furanocoumarins rather than flavonoids are the ingredients causing the various drug interactions.^[9][10]

Drugs that may be affected include oxycodone, midazolam, ciclosporin, lovastatin, methadone, dextromethorphan, simvastatin, pravastatin, felodipine, sildenafil (Viagra) and caffeine, as well as a number of antihistamines including astemizole and terfenadine.^[11]

Some Benzodiazepines have also been reported to increase both the bioavailability of Diazepam and greatly slow the rate of metabolisation.^[12] An easy way to tell if a medication may be affected by grapefruit juice is by researching whether another known CYP3A4 inhibitor drug is already contraindicated with the active drug of the medication in question. Examples of such known CYP3A4 inhibitors include cisapride (Propulsid), erythromycin, itraconazole (Sporanox), ketoconazole (Nizoral), and mibefradil (Posicor)^{[citation needed]}.

The flavonoid existing in highest concentration in grapefruit juice is naringin, which in humans is metabolised to naringenin. Other flavonoids exist in grapefruit juice in lower concentrations as well. Orange juice does not contain naringin in as high a concentration, instead containing hesperetin. It is sometimes recommended as a substitute. Juice of limes and Seville oranges can also inhibit drug metabolism, however, as can apple juice with some drugs.^[10]

Breast cancer link

A recent study published in the July 2007 edition of the British Journal of Cancer reported that eating grapefruit every day could raise the risk of developing breast cancer by almost a third. The Study found that in the test subjects, 50,000 post-menopausal women, eating just a quarter of a grapefruit daily raised the risk by up to 30%. It is believed that the fruit boosts the levels of estrogen, which in turn increases the risk of developing the disease.^[13]

See also

• Grapefruit spoon

References

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