Stronger warning on grapefruit interactions
11 April 2003
Grapefruit and its juice should be entirely off the menu for patients taking certain medications, according to revised advice from Australian health authorities.
The Adverse Drug Reactions Advisory Committee (ADRAC) last week changed advice issued only 3 months ago, which included options such as drinking grapefruit juice daily so long as drug doses were adjusted.
Now ADRAC considers that 'the safest course is to avoid grapefruit and its juice altogether when taking medicines that interact'.
The advice also applied to Seville oranges, said Dr Richard Hill, acting ADRAC unit director.
The amendment was made after the committee considered several studies that were not included in its initial literature review.
Grapefruit juice may, in some people, interact with medications that are metabolised by certain gut-wall enzymes, leading to an unexpected increase in the pharmacological effect of the medication.
The juice seems to selectively inhibit CYP3A4, a drug metabolising enzyme in the small intestine.
For patients on some calcium channel blockers (a medication that treats high blood pressure), for example, this could lead to sudden hypotension (low blood pressure).
ADRAC member Professor Gillian Shenfield, a Sydney clinical pharmacologist, said studies suggested a theoretical potential for grapefruit juice to have an interacting effect for up to 3 days after ingestion, particularly with daily consumption.
'Although there are no case reports from anywhere in the world of people taking the juice more than a couple of hours separate [from the drug] and getting into strife, to be consistent with the literature, and to be 100 per cent safe, the best advice is 'just don't do it',' Professor Shenfield said.
(Ask your doctor or pharmacist whether you can consume grapefruit or its juice with the medications you have been prescribed.)
Last Reviewed: 14 April 2003
- 1. Medical Observer Weekly 11/4/03
