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29-11-2012 | Article

Grapefruit drug clashes soar


CMAJ 2012; Advance online publication

The number of available drugs that have the potential to interact adversely with grapefruit has risen markedly in recent years, shows a review.

Canadian researchers found the number of medications that can cause serious adverse effects on interaction with grapefruit increased from 17 to 43 between 2008 and 2012.

Study authors Dr David Bailey (Lawson Health Research Institute, London, Ontario) and colleagues say that many of the drugs are widely prescribed, yet doctors lack awareness of the potential problem.

"Unless healthcare professionals are aware of the possibility that the adverse event they are seeing might have an origin in the recent addition of grapefruit to the patient's diet, it is very unlikely they will investigate it," the researchers write in the Canadian Medical Association Journal. "In addition, the patient may not volunteer this information."

The interaction is due to components of grapefruit, furanocoumarins, also found in other citrus fruits such as Seville oranges and limes. They interfere with the cytochrome P450 3A4 (CYP3A4) enzyme, which is essential for the bioinactivation of about 50% of all medications. Just a 200 ml glass of grapefruit juice can cause a clinically relevant increase in systemic drug levels, the authors explain, even if the medication is not taken at the same time.

Serious adverse effects include torsade de pointes, acute kidney failure, respiratory depression and gastrointestinal bleeding, as well as bone marrow suppression in immunocomprised patients. The team highlights that drugs with a very high predicted risk of interaction include halofantrine, maraviroc, lovastatin, simvastatin, dronedarone, ketamine, lurasidone and domperidone.

Elderly people may be particularly at risk because they are more likely to buy grapefruit products and to be taking medications than younger patients. Also, their capacity to compensate for excess drug concentrations is reduced.

Medical News is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2012

By Caroline Price