Grapefruit juice



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

Drug interactions
Grapefruit juice, and grapefruit in general, is a potent inhibitor of the Cytochrome_P450 enzyme CYP3A4, which can impact the metabolism of a variety of drugs, increasing their bioavailability. In some cases, this can lead to a fatal interaction with drugs like Astemizole. 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.

Recently some researchers have shown that furanocoumarins rather than flavinoids may be the ingredients causing the various drug interactions. http://www.hon.ch/News/HSN/532584.html

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

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 drug in question. Examples of such known CYP3A4 inhibitors include cisapride (Propulsid), erythromycin, itraconazole (Sporanox), ketoconazole (Nizoral), and mibefradil (Posicor).

The flavonoid existing in highest concentration in grapefruit juice is naringin, which in humans is metabolized 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.

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 50%. It is believed that the fruit boosts the levels of estrogen, which in turn increases the risk of developing the disease.