A news report in The Lancet provides evidence that grapefruit juice is not as beneficial as previously thought. Earlier studies indicated that grapefruit juice improved the absorption rate of some orally administered drugs. Yet now scientists are claiming that grapefruit juice could actually block the absorption of some drugs including medication prescribed to treat cancer, hypertension, allergies and heart disease.
In the case of HIV-1 protease inhibitors and some calcium-channel blockers, earlier studies demonstrated that grapefruit juice was indeed beneficial. Grapefruit juice inactivates the enzyme CYP3A4 which is the main enzyme responsible for metabolising drugs in the intestines. By inactivating the enzyme, grapefruit juice prevents the medication from being broken down before it has a chance to be absorbed.
Now the bad news. Researchers from the University of California at San Francisco have revealed another function of grapefruit juice. It activates a protein ejection mechanism (efflux pump P-glycoprotein) which actually pushes the drug molecules right out of the intestinal wall and back into the intestine.
So far, they have found that combining grapefruit juice with vinblastine, cyclosporine, losartan, digoxin and fexofenadine decreased absorption rates. In fact, grapefruit juice caused the rate of vinblastine ejection to increase six-fold.
Although the current experiment still has to be confirmed, the researchers suggest a way of working around the downside of grapefruit juice. They believe that drinking grapefruit juice about two hours before taking the medication could help. This way, the medication will not be subjected to the pumping effect while at the same time, the medication will benefit from the lasting effect of CYP34A inhibition.
In the case of HIV-1 protease inhibitors and some calcium-channel blockers, earlier studies demonstrated that grapefruit juice was indeed beneficial. Grapefruit juice inactivates the enzyme CYP3A4 which is the main enzyme responsible for metabolising drugs in the intestines. By inactivating the enzyme, grapefruit juice prevents the medication from being broken down before it has a chance to be absorbed.
Now the bad news. Researchers from the University of California at San Francisco have revealed another function of grapefruit juice. It activates a protein ejection mechanism (efflux pump P-glycoprotein) which actually pushes the drug molecules right out of the intestinal wall and back into the intestine.
So far, they have found that combining grapefruit juice with vinblastine, cyclosporine, losartan, digoxin and fexofenadine decreased absorption rates. In fact, grapefruit juice caused the rate of vinblastine ejection to increase six-fold.
Although the current experiment still has to be confirmed, the researchers suggest a way of working around the downside of grapefruit juice. They believe that drinking grapefruit juice about two hours before taking the medication could help. This way, the medication will not be subjected to the pumping effect while at the same time, the medication will benefit from the lasting effect of CYP34A inhibition.
