Grapefruit juice

Grapefruit juice is the fruit juice coming 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.^[1][2]

Drug interactions

Main article: List of drugs affected by grapefruit

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.^{[3][4][5][6][7]} In some cases, this can lead to a fatal interaction with drugs like Astemizole.^[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] Grapefruit juice has been found to interact with many drugs taken orally. Compounds in the juice including bergamottin, dihydroxybergamottin, and some flavonoids such as naringin affect the activity of certain intestinal enzymes including CYP3A4 and CYP1A2. These cytochrome P450 enzymes, which metabolize many drugs, are inhibited by grapefruit juice. As a result, serum drug concentrations increase and may become toxic. This is particularly dangerous when the drug in question has a low therapeutic index, so that a small increase in blood concentration can be the difference between therapeutic success and toxicity. Grapefruit juice only inhibits the enzyme within the intestines, not elsewhere (the liver, for instance). Therefore, it does not affect injected drugs. The degree of the effect varies widely between individuals and between samples of juice, therefore it cannot be accounted for a priori. 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 ^[9] 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. ^[10] 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. ^[9]

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. ^[11]

See also

• Grapefruit spoon

References