Eating grapefruit with some prescription drugs 'can be deadly'

Canadian scientists who discovered the interactions more than 20 years ago, looked at the latest research to help doctors better understand the serious effects the common food can have when consumed with certain prescription drugs .

Dr David Bailey said: "Many of the drugs that interact with grapefruit are highly prescribed and are essential for the treatment of important or common medical conditions.

"Recently, however, a disturbing trend has been seen. Between 2008 and 2012, the number of medications with the potential to interact with grapefruit and cause serious adverse effects...has increased from 17 to 43, representing an average rate of increase exceeding 6 drugs per year.

"This increase is a result of the introduction of new chemical entities and formulations.

"Unless health care 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 that they will investigate it.

"In addition, the patient may not volunteer this information. Thus, we contend that there remains a lack of knowledge about this interaction in the general healthcare community."

Other citrus fruits such as Seville oranges, often used in marmalade, limes and pomelos also contain furanocoumarins.

These chemicals are innate to the fruit and cause the interaction by irreversible inhibition of the drug metabolizing CYP3A4 enzyme that normally inactivates the effects of an estimated 50% of all medication.

Drugs that interact with these chemicals have three characteristics: they are administered orally, they have very low to intermediate bioavailability - percentage of the oral dose of drug absorbed into the blood circulation unchanged - and they undergo drug metabolism in the gastrointestinal tract by CYP3A4.

For drugs with very low bioavailability, ingestion of a single normal amount of grapefruit can be analogous to consuming multiple doses of the drug alone.

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Eating grapefruit with some prescription drugs 'can be deadly'