Healthy living
Body matters
When juice and drugs don't mix
Grapefruit and some other fruit juices can stop some medications from working properly
Health professionals have long known that grapefruit juice can increase the absorption of certain drugs, making normal doses potentially dangerous. Now research has emerged suggesting that grapefruit and other fruit juices may have the opposite effect, and actually decrease the absorption of other drugs making them less effective.
Almost 20 years ago researchers from the University of Western Ontario in Canada found that grapefruit juice could dramatically increase the levels of the high-blood-pressure drug felodipine. Since then scientists have pinpointed over 50 other drug interactions with grapefruit juice including statins like simvastatin, beta blockers like atenolol and certain antibiotics.
As a result of this so-called 'Grapefruit Juice Effect' many medications now carry warnings advising people to avoid grapefruit while taking the drug.
The latest study from the same team, which was presented at the American Chemical Society conference, looked at fexofenadine – an antihistamine used to combat allergies. Volunteers were given the drug with either a glass of grapefruit juice, water containing naringin (the substance in grapefruit juice that gives it the bitter taste) or plain water. When the medication was taken with the grapefruit juice 50 per cent less of the drug was absorbed compared with plain water.
"Recently, we discovered that grapefruit and these other fruit juices substantially decrease the oral absorption of certain drugs,' said team leader Dr David G Bailey. He expressed concern that absorbing less than the dose prescribed could significantly affect the performance of drugs taken for serious conditions such as cancer and high blood pressure.
The researchers believe that the active ingredient, naringin, is responsible for interfering with the absorption of the drug into the bloodstream. Bailey warns that orange and apple juices contain similar chemicals and so may well have the same effect. ‘This is just the tip of the iceberg,' says Bailey. 'I'm sure we'll find more and more drugs that are affected this way.'
Bailey advises that patients speak to their doctor or pharmacist before taking any medication with fruit juices. And to be on the safe side, he recommends taking most medication with water.
The British Heart Foundation advises that people who are taking the statin simvastatin should avoid grapefruit or grapefruit juice altogether as even small quantities can increase the potency of the drug. Not all statins are affected in the same way but it is advisable to check with your doctor or pharmacist if you have any concerns. They also warn against taking cranberry juice with the blood-thinning drug warfarin as it may increase blood clotting times.
However, for those on other medications there's no need to stop drinking fruit juice completely. "Most medication that is taken orally is absorbed by the body within 30 minutes to an hour," says Dr Stuart Patterson, lecturer in Pharmacology at King's College London. "If you consider that you can take a tablet such as aspirin every four hours, this time frame reflects how quickly the body absorbs and then removes medication from the body.
"Always take any medication with water but after that, leaving around half an hour to an hour before having any fruit juice should be sufficient to prevent any adverse interactions between your tablets and any fruit juice."
Website: British Heart Foundation www.bhf.org.uk
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Information on this site is for interest only and is not a substitute for professional medical advice. You should consult your own doctor about any specific health concerns.
