Washington, Aug 20 : Researchers at the University of Western Ontario in London, have found that grapefruit and other common fruit juices, including orange and apple, substantially decrease the absorption of certain drugs, potentially wiping out their beneficial effects.
Scientists and consumers have always thought that grapefruit juice can increase the absorption of certain drugs - with the potential for turning normal doses into toxic overdoses.
Now, the researcher who first identified this interaction is reporting new evidence that grapefruit and other common fruit juices could, in fact, have the opposite effect.
The researcher said that the study provides a new reason to avoid drinking grapefruit juice and these other juices when taking certain drugs, including some that are prescribed for fighting life-threatening conditions such as heart disease, cancer, organ-transplant rejection, and infection.
"Recently, we discovered that grapefruit and these other fruit juices substantially decrease the oral absorption of certain drugs undergoing intestinal uptake transport," says study leader David G. Bailey, Ph.D., a professor of clinical pharmacology with the University of Western Ontario in London, Ontario.
"The concern is loss of benefit of medications essential for the treatment of serious medical conditions," he added.
Almost 20 years ago, Bailey and colleagues announced the unexpected finding that grapefruit juice can dramatically boost the body's levels of the high-blood-pressure drug felodipine, causing potentially dangerous effects from excessive drug concentrations in the blood.
Since then, other researchers have identified nearly 50 medications that carry the risk of grapefruit-induced drug-overdose interactions.
As a result of the so-called "Grapefruit Juice Effect," some prescription drugs now carry warning labels against taking grapefruit juice or fresh grapefruit during drug consumption.
In the most recent research, Bailey's group had healthy volunteers take fexofenadine, an antihistamine used to fight allergies.
The volunteers consumed the drug with either a single glass of grapefruit juice, water containing only naringin (substance in grapefruit juice that gives the juice its bitter taste), or water.
Bailey said that when fexofenadine was taken with grapefruit juice, only half of the drug was absorbed compared to taking the drug with water alone.
Loosing half of the amount of drugs taken into the body can be critical for the performance certain drugs, he added.
They also showed that the active ingredient of grapefruit juice, naringin, appears to block a key drug uptake transporter, called OATP1A2, involved in shuttling drugs from the small intestine to the bloodstream.
The researchers said that blocking this transporter reduces drug absorption and neutralizes their potential benefits.
On contrary, drugs whose levels are boosted in the presence of grapefruit juice appear to block an important drug metabolizing enzyme, called CYP3A4, that normally breaks down drugs.
"This is just the tip of the iceberg. I'm sure we'll find more and more drugs that are affected this way," Bailey said.
The study was presented at the 236th National Meeting of the American Chemical Society.