Grapefruit Juice make your oral steroids more potent

Grapefruit Juice make your oral steroids more potent

A glass of grapefruit juice not only helps the oral steroids go down, it also makes it more potent. Now, a study in the current Journal of Clinical Investigation has revealed why: A substance in the juice fights a drug-degrading enzyme in the intestine. The insight could be a first step toward increasing the effectiveness of some oral drugs.

About 3 years ago, researchers noted that grapefruit juice helps the body absorb many types of drugs, including sedatives, hormones, and protease inhibitors. A group of doctors from the University of Michigan and the London Health Sciences Centre, in London, Ontario, set out to investigate. They focused on an enzyme in the liver and intestine, called CYP3A4, that usually breaks down toxins from spoiled food. “It’s [also] the most prolific of the drug-degrading enzymes,” says Paul Watkins, a member of the Michigan team. In fact, it contributes to the breakdown of about half of all known human drugs.

Watkins and his colleagues gave felodipine, a calcium channel blocker used to control high blood pressure, to 10 healthy men, both with and without grapefruit juice. The grapefruit juice increased blood concentrations of felodipine more than fourfold. The team also measured the concentrations of CYP3A4 levels in the intestine and found that they fell by 62%. Something in grapefruit juice appears to be blocking the action of CYP3A4. But the concentration of CYP3A4 in the liver was unchanged–suggesting that the juice does not affect the rate at which the drug is metabolized once it enters the bloodstream.

If the active ingredient of grapefruit juice can be identified and isolated, drugs might be made more effective–and less expensive per useful dose. Adding grapefruit’s CYP3A4 blocker to a pill could also assure a set dosage, an advantage, because people naturally vary 10-fold in how much of a drug they absorb. “It will make a lot of difference in the way people take drugs,” predicts Raymond Woosley, a pharmacologist at Georgetown University Medical Center

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