A research team headed by Dr David G. Bailey, a professor of clinical pharmacology at the University of Western Ontario, has discovered that consuming certain medications with certain fruit juices can increase or decrease their effectiveness.

Fruit juices like grapefruit, orange and apple juice, contain substances that reduce the effectiveness of common drugs, used to treat infections, allergy, transplant rejection, cancer, and high blood pressure.

As far back as 1991 Bailey and colleagues discovered that grapefruit juice slows down a liver enzyme, responsible for deactivation of blood pressure drug Felodipine (Plendil), leading to dangerously high concentrations of this drug in the blood. Later, the so-called "grapefruit juice effect'', was observed in interaction with about 40 other drugs as well.

Now, new evidence is suggesting that some other common fruit juices, including orange and apple juice in addition to grapefruit juice can also have the opposite effect. They can reduce the efficacy of some drugs by decreasing their absorption from the intestines.

Substances naringin and hesperidin seem to be the culprit in these interactions. Naringin is found in grapefruit and hesperidin in orange juice. Both compounds appear to block gut transporter molecule OATP1A2, which is responsible for the absorption from the small intestine into the bloodstream. The interfering substance in apple juice is still unidentified.

Grapefruit can change drug effects by two mechanisms; either by blocking the drug metabolism in the liver, which can lead to a toxic overdose, or impairing the drug absorption from the intestines, therefore lowering its concentration in the blood and its effectiveness.

These fruit juices have been shown to lower the absorption of anticancer agent etoposide, certain beta blockers, which are used to lower blood pressure (atenolol, celiprolol, talinolol), transplant rejection drug cyclosporine, certain antibiotics and antifungals (ciprofloxacin, levofloxacin, itraconazole) and fexofenadine, an allergy drug.

According to Bailey, "this is just the tip of the iceberg." He's convinced there are many more drugs that are affected in this way.

To avoid unwanted interactions, it is always best to take pills with water only. Before taking any medications with fruit juices or consuming them with whole fruits, consult your doctor or pharmacist.

E.Z.