Warning over risk of grapefruit clash with prescriptions

Grapefuit contain chemicals that can interact with certain drugs, making them more potent, say scientists writing in the Canadian Medical Association Journal (David Silverman/Getty Images)

Grapefruit poses a potentially lethal health risk to increasing numbers of patients taking prescription drugs, experts have warned.

Grapefruit poses a potentially lethal health risk to increasing numbers of patients taking prescription drugs, experts have warned.

The fruit contains chemicals that can interact with certain drugs, making them more potent.

Adverse effects can include acute kidney failure, respiratory failure, internal bleeding and sudden death.

While it is well known that some patients should avoid grapefruit, or grapefruit juice, the list of drugs involved has risen sharply in recent years.

Between 2008 and 2012 the number of medications with the potential to cause serious harm by interacting with grapefruit increased from 17 to 43, said scientists writing in the Canadian Medical Association Journal.

Each year, more than six of these drugs on average were being made available to patients.

Dr David Bailey, from Lawson Health Research Institute in London, Ontario, and colleagues described the trend as “disturbing”.

They wrote: “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 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.”

More than 85 drugs in total can interact with grapefruit, and of these 43 can have serious side effects, said the researchers.

Other citrus fruits such as Seville oranges, used to make marmalade, and limes contained the same active ingredients that caused the drug interactions.

The chemicals, called furanocoumarins, act on an enzyme in the gut that normally reduces the potency of medication. This can effectively boost the dose of some drugs many times.

The list of danger medicines includes treatments for anxiety, depression, allergy, HIV infection, seizures, heart rhythm abnormalities and high cholesterol.

A modest single helping of grapefruit can have an effect even if consumed hours before a drug is taken, said the scientists.

Frequent exposure to grapefruit could make matters worse. Combining the cholesterol-lowering drug simvastatin with a 200 millilitre glass of grapefruit juice once a day for three days more than tripled its concentration level.

Older people with a reduced ability to tolerate drug overdoses were at greatest risk.

“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,” the experts concluded.