Grapefruit juice

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Grapefruit juice is the fruit juice coming from grapefruits. It is rich with Vitamin C and is slightly sour. Variations include pink grapefruit juice.

[edit] Pharmacological effects

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. 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. <ref name="nyt"> Bakalar, Nicholas. "Experts Reveal the Secret Powers of Grapefruit Juice", The New York Times, 2006-03-21, p. F6. Retrieved on 2006-11-21. (in English) </ref>

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. <ref> http://abello.dic.uchile.cl/~hechavez/articulos/grapefru.htm. </ref>

An easy way to tell if a medication may 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. <ref name="nyt"/>

[edit] References

• USDA Database of Flavonoid content of food
• Arayne M, Sultana N, Bibi Z (2005). "Grape fruit juice-drug interactions.". Pak J Pharm Sci 18 (4): 45-57. PMID 16380358.

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[edit] External links

• World Famous Dole Grapefruit Juicezh:葡萄柚汁

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