Why Grapefruit Affects Some Drugs
Scientists Spot Natural Chemicals in Grapefruit That Raise Drug's Effect
WebMD News Archive
May 9, 2006 -- Researchers may have figured out why grapefruit and
grapefruit juice interact with some types of drugs.
Grapefruit may interact with some drugs for cholesterol, blood pressure,
heart rhythm, depression, anxiety,
HIV, immunosuppression, allergies, impotence, and seizures.
Grapefruit contains natural chemicals called furanocoumarins that may explain
the interaction, at least with one particular drug, Plendil, scientists report
in The American Journal of Clinical Nutrition.
It's not yet clear if furanocoumarins are also responsible for interactions
between grapefruit and other drugs, note Mary Paine, PhD, and colleagues from
the University of North Carolina at Chapel Hill.
If so, it might be possible to isolate furanocoumarins from grapefruit
juice, the researchers write.
Paine's study included 18 healthy, nonsmoking adults who were in their mid
to late 30s, on average.
After carefully screening participants (including pregnancy tests for the
nine women enrolled in the study), the researchers asked participants to avoid
products containing grapefruit.
At least a week later, participants reported to the research center after
fasting overnight. They took a 10-milligram tablet of Plendil with a glass of
regular grapefruit juice, orange juice, or furanocoumarin-free grapefruit
Plendil is a calcium channel blocker, a type of drug used to treat heart disease
and high blood
Participants tried one drink per session. Sessions were held at least a week
The researchers made the furanocoumarin-free grapefruit juice in their lab.
They checked to make sure it was free of furanocoumarins. The drink was
"sweeter and less bitter" than the regular grapefruit juice, write
Paine and colleagues.
Participants stayed at the research center overnight. Every few hours, the
researchers checked participants' blood samples for Plendil levels.
As expected, maximum blood concentrations of Plendil were higher when the
drug was taken with regular grapefruit juice. Blood concentrations of Plendil
didn't spike with orange juice - which doesn't react with Plendil like
grapefruit juice -- or furanocoumarin-free grapefruit juice.
The Plendil and juice treatments were "generally well tolerated,"
the researchers note. They add that none of the participants commented on the
taste of the furanocoumarin-free grapefruit juice.
The study only tested Plendil and grapefruit juice.
If furanocoumarins prove to be responsible for other grapefruit-drug
reactions, creating commercially available furanocoumarin-free grapefruit juice
"could provide an alternative for patients who are taking medications with
interaction potential," write Paine and colleagues.
Check with your doctor about potential interactions between grapefruit and
any drugs you take.