Six years ago, Canadian researchers found another benefit of grapefruit.
They discovered, quite by accident, that people who sloshed down their high blood pressure medicine with a glass of grapefruit juice got an extra kick: The drug became much more effective, apparently because it was absorbed better by the body.
So much more effective, in fact, that some doctors now worry that people who usually use water to take certain calcium channel blockers might wind up lowering their blood pressure too steeply if they suddenly switch to grapefruit juice.
Then there’s the case of the young Michigan man who reportedly died of cardiac arrythmia soon after taking Seldane, the antihistamine/decongestant, with two glasses of grapefruit juice.
“The cause of his death is that he took Seldane with grapefruit juice,” said Dr. J. David Spence, one of the Canadian researchers and director of stroke prevention and atherosclerosis research at the Robarts Research Institute in London, Ontario.
Others, among them Dr. David Flockhart, associate director of the division of clinical pharmacology at Georgetown University Medical Center in Washington, say that after two studies on Seldane and grapefruit juice, the evidence remains inconclusive.
Nonetheless, Hoechst Marion Roussel, the manufacturer of Seldane, added a warning to package labels in May advising people not to take the pill with grapefruit.
Who’d-a-thunk it? Good old grapefruit, that mouth-zinging staple of many a breakfast table, cast in the role of nutritional bad guy!
Yet the “grapefruit effect” has been a source of concern for several years, and University of Michigan researchers recently said they had discovered the reason why.
Unlike oranges and other citrus fruits, grapefruit–in juice form and in wedges–contains two types of chemicals called furanocoumarins, says Dr. Paul B. Watkins, director of the University of Michigan General Clinical Research Center in Ann Arbor.
These substances trigger the drug-potentiating effect by interacting with an enzyme (called CYP3A4) in the intestinal walls. Normally, this enzyme breaks down some, though not all, drugs as they pass through the digestive system, Watkins says, adding that this is a problem for drug manufacturers because the enzyme makes it tough to get adequate quantities of some medications into the bloodstream.
When grapefruit juice is present–and some researchers think its effects can linger for a day or more–the enzyme is knocked out of commission and absorption of certain drugs is dramatically increased, sometimes by as much as nine times.
With the immunosuppressant cyclosporin, grapefruit juice boosts absorption so much that some patients who take the drug to prevent rejection of a transplanted organ can get the same effect with less medication.
Dr. Ray Woosley, chairman of the pharmacology department and co-director of the Cardiovascular Institute at Georgetown, says that when his brother, a kidney transplant patient, began taking grapefruit juice along with cyclosporin, he was able to cut the cost of his medication from $12,000 a year to $6,000.
Cholesterol-lowering drugs such as lovastatin and simvastatin, as well as a drug called Propulsid for gastrointestinal reflux, may interact with grapefruit juice, too, although this is not so well studied.
So far, none of this constitutes a huge public-health concern, says Watkins, because many drugs are designed to be safe even at high blood levels. This is especially true for drugs whose absorption rates vary.
Still, it gets tricky trying to figure out just how much grapefruit juice may affect drug metabolism in a given patient. Part of the difficulty is that the quantity of active ingredients in grapefruit varies considerably–between grapefruit products and even between different lots of the same brand of frozen concentrate.
Furthermore, people vary widely in how much of the intestinal enzyme they produce.
“If you have a lot of this enzyme,” Watkins said, “you won’t get much of certain drugs into your body. Therefore, taking grapefruit juice will have a big effect. If you have low amounts of this enzyme, you will already be absorbing higher amounts of drugs and grapefruit juice will add little effect.”
Unfortunately, there is no easy way consumers can gauge their enzyme levels.
So what should you do until the scientists sort it all out?
The safest course is to not change what you’re doing. If you have been taking your pills with grapefruit juice for years and have had no problems, keep on doing so. If you haven’t, don’t start.
If you’re curious about a particular combination, ask your pharmacist to look up potential interactions.
