It has been common knowledge for a number of years that grapefruit juice can influence the absorption of certain drugs, potentially turning normal doses into toxic overdoses.
Now scientists say that grapefruit and other fruit juices such as orange and apple, can have the opposite effect by substantially decreasing the absorption of other drugs, potentially eliminating their intended beneficial effects.
This new evidence comes from the same researcher, Professor David G. Bailey, who made the discovery about the interaction between grapefruit and certain drugs.
This latest research has found that grapefruit juice and other juices decrease the oral absorption of certain drugs such as those prescribed for fighting life-threatening conditions such as heart disease, cancer, organ-transplant rejection, and serious infections.
The researchers say these drinks should be avoided by patients taking such drugs.
The new study represents the first controlled human studies of this type of drug-lowering interaction and Dr. Bailey the study leader, a professor of clinical pharmacology with the University of Western Ontario in London, Ontario, says the concern is the loss of benefit of medications essential for the treatment of serious medical conditions.
It was almost 20 years ago that Dr. Bailey and his colleagues found 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.
Other researchers have since identified almost 50 medications that carry the risk of grapefruit-induced drug-overdose interactions and now some prescription drugs carry warning labels against taking grapefruit juice or fresh grapefruit during the drugs' consumption.
For this recent research, Bailey's team had healthy volunteers take fexofenadine, an antihistamine used to fight allergies, along 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.
They found that when fexofenadine was taken with grapefruit juice, only half of the drug was absorbed compared to taking the drug with water alone.
Dr. Bailey says the loss of half of the amount of drugs taken into the body can be critical for the performance of certain drugs, and he believes this the mere beginning and that there are more drugs which are affected this way.
The research also showed that the active ingredient of grapefruit juice, naringin, appears to block a key drug uptake transporter called OATP1A2, which is involved in shuttling drugs from the small intestine to the bloodstream, this action reduces drug absorption and neutralizes their potential benefits.