(un)Healthy drink

The ideal fruit juice plays havoc with the body's ability to absorb medicines

Published: Thursday 15 July 1999

Grape-fruit juice and medicati some patients may find it strange advice to be told to keep off fruit juice while taking medications. But that is precisely what doctors are telling some sick people -- to stay off grape-fruit juice. Evidence is mounting to show that drinking a glass of grape-fruit juice with some medicines plays havoc with their health as the drugs taken go berserk, instead of having the intended effect on the diseased organ or system.

Interestingly, this juice either increases the quantity of the drug thus creating an excess of the drug and the associated toxicity or prevents their efficacy by reducing the body's absorption of certain drugs. Scientists at the University of California at San Francisco ( ucsf ) report that grape-fruit juice may have a negative impact on the body's absorption of many widely-prescribed medications. In a study just published, Andrea Soldner and his team demonstrate that grape-fruit juice can actually inhibit the body's absorption of certain drugs including:

- Vinblastine (combats cancer)

- Cyclosporine (suppresses organ rejection following transplant)

- Losartan (controls high blood pressure)

- Digoxin (treats congestive heart failure)

- Fexofenadine (alleviates allergy symptoms)

This inhibition occurs because an unknown substance in grape-fruit juice activates one of the body's naturally-produced drug efflux mechanisms, known as P-glycoprotein, located in the intestinal tract. When grape-fruit juice interacts with P-glycoprotein, the result is an increased likelihood that certain drugs will be stopped from entering the bloodstream. ( Pharmaceutical Research , Vol 16, No 4). "These findings help to clarify some major discrepancies we've noticed in the impact of grape-fruit juice on various types of medications," says Leslie Benet, professor of Biopharmaceutical Sciences at ucsf and director of the study. He, however, suggests that patients already taking grape-fruit juice with their medications can continue to do so.

According to Benet, "Patients who have not previously taken their drugs with grape-fruit juice should be very cautious in doing so. We now recognise, that, depending on the drug, grape-fruit juice may either increase or decrease levels of drug in the blood, leading to potential concerns for toxicity or lack of efficacy."

Grape-fruit juice is also known to improve the oral absorption of several important medications on the market by decreasing levels of an intestinal enzyme, known as cyp3a4 , that would otherwise breakdown drug molecules before they reach the blood stream. Patients should not take the epilepsy drug carbamazepine or the high blood pressure medication felodipine with grape-fruit juice as also hiv -protease inhibitors - saquinavir sold as Invirase. Compounds in grape-fruit and other citrus fruits inhibit certain enzymes that help break down, or metabolise, a variety of medications.

Consequently, taking these drugs with these juices boosts concentrations of the drugs in the bloodstream -- to potentially harmful levels. It is for this reason that clinicians have been warning consumers against taking the antihistamine terfenadine (sold under the name Seldane) with grape-fruit juice. Researchers have also found that taking the cholesterol-lowering drug lovastatin, the post-transplant medication cyclosporin, and calcium channel blockers -- commonly prescribed for heart disease -- with grape-fruit juice increases levels of these medications in the bloodstream.

In another study, researchers Santosh K Garg and colleagues at the Postgraduate Institute of Medical Education and Research, in Chandigarh, report similar findings with the anticonvulsant drug carbamazepine. Patients who took the drug with grape-fruit juice had "significantly increased" concentrations in their blood, the researchers claim. In the light of these findings, clinicians should "instruct patients receiving carbamazepine therapy to avoid consumption of citrus fruits, especially grape-fruit, to avoid undue adverse effects,'' wrote the researchers ( Clinical Pharmacology and Therapeutics , Vol 64, No 3).

Similarly, older patients prescribed felodipine should avoid taking the drug with grape-fruit juice, according to a study presented at the annual meeting of the American College of Clinical Pharmacology. Elderly patients who took the medication with grape-fruit juice had blood levels of the drug that were 3.5 times higher than normal, George Dresser of the University of Western Ontario in Canada, reported. These levels can cause a more marked drop in blood pressure, which may be dangerous, Dresser said.

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