According to a report in the Southern Medical Journal, grapefruit juice is a well-documented inhibitor of a specific enzyme (CYP3A4 isoenzyme) involved in the metabolism of over 50% of commonly prescribed drugs.
Americans consume grapefruit juice in large quantities, with 14% of the population drinking grapefruit juice weekly.
The report documented an unusual case of verapamil (a blood pressure drug) toxicity in a 42-year-old female.
The New York Times claims the 42-year-old was barely responding when her husband brought her to the emergency room.
“Her heart rate was slowing, and her blood pressure was falling. Doctors had to insert a breathing tube, and then a pacemaker, to revive her.”
“The culprit was grapefruit juice,” said Dr. Unni Pillai, a nephrologist in St. Louis, Mo., who treated the woman several years ago and later published a case report.
“She loved grapefruit juice, and she had such a bad migraine, with nausea and vomiting, that she could not tolerate anything else.”
As New York Times writer Roni Caryn Ranin points out, the previous week, she survived mainly on grapefruit juice.
“Then she took verapamil, one of dozens of drugs whose potency is dramatically increased if taken with grapefruit, and in her case, the interaction was life-threatening.”
Ranin notes that under normal circumstances, the drugs are metabolized in the gastrointestinal tract, and relatively little is absorbed, because an enzyme (CYP3A4) deactivates them.
“But grapefruit contains natural chemicals called furanocoumarins, that inhibit the enzyme, and without it the gut absorbs much more of a drug and blood levels rise dramatically.”
Dr. David Bailey, a Canadian researcher who first described this interaction more than two decades ago, released an updated list of medications affected by grapefruit.
Bailey says there are now 85 such drugs on the market, including common cholesterol-lowering drugs, new anticancer agents, and some synthetic opiates and psychiatric drugs, as well as certain immunosuppressant medications taken by organ transplant patients, some AIDS medications, and some birth control pills and estrogen treatments.
“What drove us to write this paper was the number of new drugs that have come out in the last four years,” said Dr. Bailey, a clinical pharmacologist at the Lawson Health Research Institute, who first discovered the interaction by accident in the 1990s.
Dr. Bailey believes many cases are missed because doctors don’t think to ask if patients are consuming grapefruit or grapefruit juice.
“The bottom line is that even if the frequency is low, the consequences can be dire,” he said. “Why do we have to have a body count before we make changes?”
For 43 of the 85 drugs now on the list, consumption with grapefruit can be life-threatening, Dr. Bailey said. Taken with grapefruit, other drugs like fentanyl, oxycodone and methadone can cause fatal respiratory depression.
Advice from experts for grapefruit lovers:
¶ If you take oral medication of any kind, check the list to see if it interacts with grapefruit. Make sure you understand the potential side effects of an interaction; if they are life-threatening or could cause permanent injury, avoid grapefruit altogether. Some drugs, such as clopidogrel, may be less effective when taken with grapefruit.
¶ If you take one of the listed drugs a regular basis, keep in mind that you may want to avoid grapefruit, as well as pomelo, lime and marmalade. Be on the lookout for symptoms that could be side effects of the drug. If you are on statins, this could be unusual muscle soreness.
¶ It is not enough to avoid taking your medicine at the same time as grapefruit. You must avoid consuming grapefruit the whole period that you are on the medication.
¶ In general, it is a good idea to avoid sudden dramatic changes in diet and extreme diets that rely on a narrow group of foods. If you can’t live without grapefruit, ask your doctor if there’s an alternative drug for you.