MONDAY, Nov. 26 (HealthDay News) -- Because of new chemical
formulations, prescription drugs that interact badly with
grapefruit have more than doubled in number since 2008, yet many
doctors seem unaware of this, Canadian researchers report.
"The number of drugs on the market with the potential to produce
serious adverse and in many cases life-threatening effects when
combined with grapefruit has markedly increased over the past few
years from 17 to 43 in four years," said lead researcher David
Bailey, from the Lawson Health Research Institute in London,
"There is much greater need for health care professionals to
understand grapefruit/drug interactions and to apply this
information to the safer use of these drugs in their clinical
practice," Bailey said.
Even small amounts of grapefruit or grapefruit juice have the
potential to cause sudden death, acute kidney failure, respiratory
failure, gastrointestinal bleeding and other serious side effects
when paired with these medications. Included are certain
cholesterol-lowering medications, blood pressure drugs, cancer
treatments and antibiotics such as erythromycin, the researchers
According to their review article, published Nov. 26 in the
Canadian Medical Association Journal, more than 85 drugs may
interact with grapefruit. Forty-three of these can have serious
side effects, the researchers said.
Citrus fruits such as limes and Seville oranges, often used in
marmalade, also contain the active ingredients -- called
furanocoumarins -- that cause the dangerous interactions, the
researchers said. The chemicals apparently inhibit an enzyme that
normally deactivates about half the effects of medication.
All the drugs that interact with these chemicals are taken
orally and don't metabolize well, meaning much of the drug passes
through the body without entering the bloodstream. All are
metabolized in the stomach in the same way, the researchers
A small amount of grapefruit, even ingested hours before taking
the medications, can increase the amount of the drug metabolized,
which is like taking many doses at once, the researchers said.
The toxic effect can build when the drug is taken repeatedly.
For example, if the cholesterol-lowering drug Zocor is combined
with a 7-ounce glass of grapefruit juice once a day for three days,
the drug in the bloodstream will increase 330 percent, Bailey
According to the report, drugs that can interact with grapefruit
include: Certain cholesterol-lowering statin drugs, such as Zocor
(simvastatin), Lipitor (atorvastatin) and Pravachol
(pravastatin),Some blood pressure-lowering drugs, such as nifedipine
(Nifediac and Afeditab),Organ transplant rejection drugs, such as cyclosporine
(Sandimmune and Neoral),Certain cardiovascular drugs, such as amiodarone (Cordarone and
Nexterone), clopidogrel and apixaban.
Because people older than 45 are the major buyers of grapefruit
and are more likely than younger individuals to take a variety of
medications, they are most at risk. Also, because of their advanced
age, they are most vulnerable to the harmful reactions of
grapefruit-drug combinations, the researchers said.
Dr. Gregg Fonarow, a spokesman for the American Heart
Association and a professor of cardiology at the University of
California, Los Angeles, said little is known about how often these
adverse effects occur in real world practice. Further studies are
necessary, he added.
"Patients taking medications where there are potentially serious
adverse interactions should, in general, be advised to avoid
consumption of moderate or large quantities of grapefruit, or
together with their physician consider potential alternative
medications that are not metabolized by the liver enzyme inhibited
by grapefruit," Fonarow said.
For more information on drug interactions, visit the
U.S. National Library of Medicine.