Since we first learned 20 years ago that grapefruits and other fruits can cause serious, life-threatening interactions with certain medications, the number of these drugs has more than doubled, yet physicians may be unaware of these risks, say Canadian researchers.
According to their report, there are over 85 drugs that interact with grapefruit and 43 that can cause serious adverse effects. These reactions include kidney or respiratory failure, gastrointestinal bleeding, renal toxicity or sudden death.
Many of these drugs that interact with grapefruit are highly prescribed and are essential for the treatment of serious or common medical conditions.
The researchers are concerned that unless health care practitioners are aware of this possibility, it is very unlikely they will consider grapefruit as the cause of the adverse effects they are observing. In addition, the patient may not be able to volunteer this information. Their report summarizes evidence to help clinicians recognize the side effects.
Grapefruits can cause both a drug overdose and make some drugs less effective.
A substance in grapefruits called furanocoumarins affects an enzyme in the gastrointestinal tract that normally inactivates the effects of 50% of all medication. So the result is an increase in drug absorption that can result in a serious overdose.
For example, simvastatin, a commonly used statin, combined with about six ounces of grapefruit juice once a day for three days, produced a 330% systemic concentration of the drug compared with water.
Another substance in grapefruit called naringin can have the opposite effect, reducing the effectiveness of drugs. Naringin-like substances are also found in orange and apple juices
Naringin has been shown to lower the absorption of fexofenadine, an antihistamine used to combat allergies, etoposide, an anticancer agent; certain beta blockers (atenolol, celiprolol, talinolol) used to treat high blood pressure and prevent heart attacks; cyclosporine, a drug taken to prevent rejection of transplanted organs; and certain antibiotics (ciprofloxacin, levofloxacin, itraconazole). But additional drugs are likely to be added to the list as physicians become more aware of this drug-lowering interaction.
Who’s at Risk
People older than 45 years are the largest purchasers of grapefruit and receive the most drug prescriptions. They are more likely to have decreased ability to tolerate excessive systemic drug concentrations as with an overdose. They can also be more susceptible to serious complications if their medication is blocked by grapefruit consumption. Consequently, older people are especially vulnerable to these interactions.
The researchers recommend that patients consult with their doctor or pharmacist before taking any medications with grapefruit juice or other juices. When in doubt, take medications with water unless contraindicated.
American Chemical Society