Grapefruit leads to overdose when combined with common drugs, study finds

Bruce DeMara 
Life Reporter 

Biting into your breakfast could be dangerous — many drugs interact negatively with grapefruit, and the consequences can be deadly. And the number of drugs affected is on the rise.

That’s the warning from a new study in the Canadian Medical Association Journal, one that is aimed at health care professionals and their patients, particularly people over 45.

“There are so many new drugs that are coming out to the market that have the capacity to produce these very extraordinarily serious side effects,” said Dr. David Bailey, lead author of the study by the Lawson Health Research Institute of London, Ont.

“We’re talking sudden death here. People think ‘Naw, that can’t happen,’ but it’s true,” he added.

The study notes that people over 45 are at the highest risk for two reasons: they’re the highest consumers of grapefruit juice and they’re more likely to be taking medications for a range of illnesses.

Bailey’s team was the first to discover the negative interaction between grapefruit juice and some drugs more than 20 years ago. Their findings were published in The Lancet, the world’s leading medical journal.

Four years ago, they found only 17 drugs had the potential to cause severe health problems. Today, the number has risen to 44 and includes an array of medications that are “highly prescribed and are essential to the treatment of important or common medical conditions,” Bailey noted.

These drugs, all taken orally, include anti-cancer drugs, including Crizotinib and Pazopanib, antibiotics, including Erythromycin and Quinine, and drugs that treat cardiovascular disease, such as Apixaban and Felodipine.

The most serious risk — sudden death — is caused by a form of heart arrhythmia known as Torsades de points. Others health impacts include acute kidney failure, respiratory failure, gastrointestinal bleeding, bone marrow suppression in people with damaged immune systems and renal toxicity.

Grapefruit juice contains compounds that suppress an essential enzyme in the digestive system called furanocoumarins.

This enzyme, vital to human health, also reduces the medication’s absorption into the bloodstream. The dosages of most drugs are based on the fact that 80 to 90 per cent of the drug will be inactivated by the enzyme.

When the enzyme is suppressed by grapefruit, the result is an unintended “overdose” of the medication to dangerous levels many times higher than the desired amount.

Other fruits, including Seville oranges, limes and pomelos, also have furanocoumarins, and while they’re not as well studied as grapefruit, the same negative effects can be inferred, Bailey noted.