Patients often are warned against taking certain pills with grapefruit juice, which can turn normal doses of a drug into a toxic overdose. Now, researchers have raised a new concern: grapefruit, orange and apple juices may also block the effects of some drugs, wiping out any potential benefit to patients, according to a new study.
Healthy volunteers took a dose of the allergy drug fexofenadine, downing it with water or juice. When the drug was taken with grapefruit juice, for instance, only half of the dose was absorbed into the bloodstream, compared to taking it with water. The findings were presented this week at the national meeting of the American Chemical Society by researchers at the University of Western Ontario in London, Ontario.
So far, the investigators have found that grapefruit, orange and apple juices reduce absorption of the anticancer drug etoposide; certain beta blockers used to treat high blood pressure; cyclosporine, used to prevent rejection of transplanted organs; and certain antibiotics. Additional drugs are likely to be added to the list, said David G. Bailey, a professor of clinical pharmacology at the University of Western Ontario.
“This is just the tip of the iceberg,” Dr. Bailey said in a press release. “I’m sure we’ll find more and more drugs that are affected this way.”
It was Dr. Bailey who originally identified the potential harm in consuming medications with grapefruit juice, showing that it can interact with drugs in a way that raises blood concentration of the medication to dangerous levels. It’s known to affect about 50 drugs, ranging from cholesterol-lowering statins to Viagra. Some drugs now carry labels warning consumers against taking them with grapefruit juice or fresh grapefruit.
Dr. Bailey said patients should consult with their doctors or pharmacists before taking any medications with grapefruit or other juices. The best advice, however, is to take most medications only with water.