This is a really good site... it's called "The grapefruit juice effect" ... there is also a list of medication here - YES, you had BETTER DRINK SOME GRAPEFRUIT JUICE WITH THOSE BENZOS ... the website:
http://pharmacology.about.com/health/pharmacology/library/weekly/aa000522a.htm
Here is part of the article -
The mechanism of the grapefruit juice effect is probably that one or more of the chemicals (most likely bioflavonoids and/or furanocoumarins) in grapefruit juice decreases the amount of (or inhibit the activity of) one or more specific enzymes in the intestinal wall and liver. These enzymes include CYP1A2, CYP3A3, and CYP3A4, which are part of the cytochrome P450 (CYP) family of enzymes. The CYP3A family of enzymes is thought to metabolize or inactivate approximately 60% of all drugs. These enzymes normally decrease the amount, via metabolism, of certain drugs which enter the systemic circulation. Thus when the enzyme is inactivated or the amount decreased, the amount of the drug entering the bloodstream is increased. This can result in increased therapeutic activity and possibly toxicity of the drug. Cytochrome p450 3A4 (CYP3A4) is currently thought to be the major enzyme affecting drug metabolism which is inhibited by grapefruit or grapefruit juice. Hence, any drug normally metabolized by that enzyme may show increased effectiveness and/or toxicity when taken with grapefruit juice. Such drugs are listed in The Grapefruit Juice Effect: Part 2 - Medications List.
Although the emphasis has been on possibly dangerous interactions of drugs and grapefruit, the interaction can also be beneficial. According to the Boston Globe, a kidney transplant patient began taking grapefruit juice along with the immunosuppressant cyclosporin, and cut the cost of his medication from $12,000 a year to $6,000. Some drug manufacturers are now trying to incorporate the active ingredients of grapefruit juice into various pills to increase their availability after oral administration. In fact, one company, AvMax, Inc., was recently issued a patent for this technology. That company hopes to develop oral dosage forms for some anticancer drugs, such as Taxol and Taxotere, which can currently be administered only intravenously.
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