Warning: Grapefruit is a Lethal Combination with Some Medications

Warning: Grapefruit is a Lethal Combination with Some Medications

Written by Alex Reid
Posted December 3, 2012

To the shock and surprise of patients and doctors everywhere, the combination of grapefruit with certain prescription medications can have deadly consequences. In an article recently published in the Canadian Medical Association Journal (CMAJ) Dr. David Bailey of Lawson Health Research Institute, London, Ont., along with his team, explore this growing problem.

After first discovering these interactions more than 20 years ago, the researchers have revisited the issue to reveal alarming changes. “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,” writes Bailey. “This increase is a result of the introduction of new chemical entities and formulations.”

The effects from this combination can be as severe as acute kidney failure, respiratory failure, gastrointestinal bleeding, bone marrow suppression, renal toxicity, and even sudden death. And the most dangerous fact is that many doctors are unlikely to identify grapefruit as the cause of these effects. According to the article, “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.”

What's worse is that the patient often won't see this as relevant information to share with their doctor. The authors state: “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.”

While there are 43 identified drugs that can have serious side effects when combined with grapefruit, over 85 drugs may interact with the food. The active ingredients contained in grapefruit (furanocoumarins) are also found in citrus fruits such as Sevilla oranges, limes, and pomelos. The interaction happens because these ingredients inhibit a natural enzyme found in the digestive tract (CYP3A4) which normally inactivates 50% of all medication. What this means is that eating grapefruit along with one of these medications is akin to taking multiple doses of the drug alone.

Even grapefruit eaten hours before the dosage is taken can have an effect, and daily consumption of the fruit can increase this effect to the extent that a drug's concentration can increase by 330% in some cases. But there are three common characteristics shared by drugs with these effects to aid in identification. First, that they are all administered orally, second is that they have very low to intermediate bioavailability (percentage of the drug absorbed into the bloodstream unchanged), and the third is that they are metabolized in the gastrointestinal tract by CPY3A4.

Persons who are most at risk for these interactions are individuals older than 45 years because they are the prime purchasers of grapefruit and receive the most prescription drugs. Until more conclusive research is done on the topic, patients on prescription drugs should watch out for grapefruit.

The article concludes:

The current trend of increasing numbers of newly marketed grapefruit-affected drugs possessing substantial adverse clinical effects necessitates an understanding of this interaction and the application of this knowledge for the safe and effective use of drugs in general practice.”