Chemical Culprit in Grapefruit-Drug Interactions Identified

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People are discouraged from consuming grapefruits or grapefruit juice while taking certain medications because they can affect the way the medications are metabolized. Now scientists are closer to understanding why this dangerous interaction occurs. Johns Hopkins Health Alerts reports on the latest research.

Johns Hopkins Health Alerts' recent Prescription Drug Health Alert reported on new research regarding the reason why grapefruit juice can potentially cause a dangerous interaction with certain of the medications you take.

FOOD AND DRUG INTERACTIONS
Certain foods and drinks don't mix well with certain medications. For example, grapefruits or grapefruit juice may interact badly with a number of medications, because natural grapefruit contains a substance that affects the activity of an enzyme in the intestines and liver that processes these medications. This could result in a dangerous increase in the level of the drug in your blood.

Another potentially dangerous interaction is between the blood thinner warfarin (Coumadin and generic brands) and vitamin K. The vitamin, present in many multivitamins and supplements, neutralizes or reduces the effect of the medication warfarin. This raises the risk of a blood clot, which the warfarin is intended to prevent.

GRAPEFRUIT AND DRUG INTERACTIONS
Now scientists have identified the specific chemical in grapefruit juice responsible for many drug-food interactions, according to an article in the American Journal of Clinical Nutrition (Volume 83, page 1097).

Previous research implicated a family of chemical compounds called furanocoumarins (FCs) as the culprit in grapefruit juice. To confirm this suspicion, the scientists created FC-free grapefruit juice and compared its effects with those of whole grapefruit juice or orange juice (the control group in the study).

GRAPEFRUIT AND DRUG INTERACTION STUDY
Eighteen study volunteers drank 8 oz of whole or FC-free juice along with a dose of felodipine (Plendil), a blood pressure medication.

The blood concentration of Plendil was nearly THREE times higher when people took it with 8 ounces of whole grapefruit juice, compared with blood levels after subjects took it with the FC-free grapefruit juice or orange juice (the control group in the study).

This means that the blood level of Plendil was higher when taken with whole grapefruit juice, potentially causing dangerously low blood pressure.

The researchers said their finding could assist in the study of other drug-food interactions.

Grapefruit has also been known to diminish the absorption of some drugs in the body. So always follow the guidelines given on your medications with regard to food and drug interactions.

One further note: In reference to the control group in the study, regular orange juice was found to be safe to drink with Plendil. However, you may want to avoid Seville oranges in juice or marmalade, as they are the only type of oranges to contain furanocoumarins.

For more free Prescription Drug Health Alerts, please visit:
Johns Hopkins Prescription Drugs Health Alerts

You can learn more about the latest research on prescription drugs in the annual Johns Hopkins Prescription Drug White Paper:
The Johns Hopkins White Paper: Prescription Drugs

Medical Disclaimer: This information is not intended to substitute for the advice of a physician.

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JOAN MULLALLY
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