Grapefruit and Drugs: The Good, the Bad, the Unknown

A couple of recent news reports support the notion that the more we know medicine, the less we know about health. The latest yes/no/maybe answer to a health question concerns grapefruit, a fruit long known to affect how our bodies process drugs.

As reported by U.S. News & World Report, patients with incurable cancer who drank 8 ounces of grapefruit juice a day enhanced the effect of a drug they were taking. The study was reported in Clinical Cancer Research.

The drug, sirolimus (Rapamune), suppressed the immune system and is not approved for treating cancer. It’s generally prescribed to prevent rejection after a kidney transplant, and to treat psoriasis. It was included in this study because its derivatives have been used to treat kidney and breast cancer.

Some study patients responded positively to the drug/juice combo-their condition stabilized for a while. With the exception of one patient, tumors did not disappear. But the primary result of the admittedly small study (about 150 patients with incurable cancer and no effective treatment) was that grapefruit juice enabled the drug to be used in smaller doses, which would reduce side effects and possibly cost.

Sirolimus has poor “bioavailabilty”-that means the body can’t use it efficiently. Only about 14 percent of it is metabolized. Because grapefruit is known for boosting the effects of other drugs, researchers wanted to see if it could improve this one’s bioavailability. And it did.

Sirolimus costs about $1,000 a month. Combine it with drinking grapefruit juice, researchers suggest, and the cost could drop to around $300 a month. The cost of other expensive cancer drugs ($3,000-$10,000 a month) also could be slashed by equivalent amounts when taken with grapefruit juice.

Lowering the dose, of course, also could reduce side effects, which include nausea and diarrhea.

But because the effects of grapefruit vary among different drugs and dosages, broad generalizations can’t be drawn, and consumers are advised not to experiment on their own.

The research is in its infancy. Grapefruit juices vary in how well they inhibit the enzymes in the liver and intestine that break down drugs, leaving more of the drug available to be metabolized, and individual biochemistry also affects absorption.

But yang to that study’s yin was noted recently by consumer organization Public Citizen’s recent Best Pills, Worst Pills newsletter. It warned that drinking grapefruit juice while taking certain medications can be really bad medicine, a cautionary tale described by

Public Citizen listed 82 medications whose effects can be altered by drinking grapefruit juice. The combination might result in some delivering too much of the drug, and others too little, the organization said. Earlier this year, the FDA reported that grapefruit juice might reduce the effectiveness of some drugs.

Among the common drugs Public Citizen identified as problematic in terms of grapefruit interaction are:

  • Lipitor;
  • Tegretol;
  • Propulsid;
  • Celexa;
  • Valium;
  • Benadryl;
  • Multaq;
  • Prozac;
  • Haldol;
  • Serzone;
  • Viracept;
  • Prilosec;
  • Paxil;
  • Seroquel;
  • Zoloft;
  • Viagra;
  • Zocor; and
  • Coumadin.

In addition to its subscription resource, Public Citizen says the National Library of Medicine’s DailyMed website offers a useful guide for drug interactions and information. And the FDA has these tips for patients who take over-the-counter or prescription drugs:

  • Ask your pharmacist or doctor if grapefruit or grapefruit juice affects absorption of the medicine. If so, ask other juices are a safer option.
  • Read the medication guide or patient information sheet that comes with your prescription medicine. Some advise not to take the drug with grapefruit juice.
  • Read the drug facts label on nonprescription medicine; it often mentions grapefruit or other fruit juices that might pose a problem.
  • If you must avoid grapefruit juice with your medicine, check the label on other fruit juice or drinks flavored with fruit juice to make sure they don’t contain grapefruit juice.
  • Seville oranges (often used to make orange marmalade) and tangelos (a cross between tangerines and grapefruit) affect the same enzyme as grapefruit juice, so avoid them if your medicine interacts with grapefruit juice.
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