|
Scientists and consumers
have known for years that grapefruit juice can increase
the absorption of certain drugs - with the potential for
turning normal doses into toxic overdoses.
|
Now, the researcher who first identified this
interaction is reporting new evidence that
grapefruit and other common fruit juices,
including orange and apple, can do the opposite
effect by substantially decreasing the
absorption of other drugs, potentially wiping
out their beneficial effects.
The study provides a new reason to avoid
drinking grapefruit juice and these other juices
when taking certain drugs, including some that
are prescribed for fighting life-threatening
conditions such as heart disease, cancer,
organ-transplant rejection, and infection, the
researcher says. These findings - representing
the first controlled human studies of this type
of drug-lowering interaction - were described
today at the 236th National Meeting of the
American Chemical Society.
|
|
|
"Recently, we discovered that grapefruit
and these other fruit juices
substantially decrease the oral
absorption of certain drugs undergoing
intestinal uptake transport," says study
leader David G. Bailey, Ph.D., a
professor of clinical pharmacology with
the University of Western Ontario in
London, Ontario. "The concern is loss of
benefit of medications essential for the
treatment of serious medical
conditions."
|
|
|
|
|
Bailey and colleagues announced almost
20 years ago the unexpected finding that
grapefruit juice can dramatically boost
the body's levels of the
high-blood-pressure drug felodipine,
causing potentially dangerous effects
from excessive drug concentrations in
the blood. Since then, other researchers
have identified nearly 50 medications
that carry the risk of
grapefruit-induced drug-overdose
interactions. As a result of the
so-called "Grapefruit Juice Effect,"
some prescription drugs now carry
warning labels against taking grapefruit
juice or fresh grapefruit during drug
consumption.
In the most recent research, Bailey's
group had healthy volunteers take
fexofenadine, an antihistamine used to
fight allergies. The volunteers consumed
the drug with either a single glass of
grapefruit juice, water containing only
naringin (substance in grapefruit juice
that gives the juice its bitter taste),
or water. When fexofenadine was taken
with grapefruit juice, only half of the
drug was absorbed compared to taking the
drug with water alone, Bailey says.
Loosing half of the amount of drugs
taken into the body can be critical for
the performance certain drugs, he points
out.
|
|
They also showed that the active ingredient of
grapefruit juice, naringin, appears to block a key drug
uptake transporter, called OATP1A2, involved in
shuttling drugs from the small intestine to the
bloodstream. Blocking this transporter reduces drug
absorption and neutralizes their potential benefits, the
researchers say. By contrast, drugs whose levels are
boosted in the presence of grapefruit juice appear to
block an important drug metabolizing enzyme, called
CYP3A4, that normally breaks down drugs.
"This is just the tip of the iceberg," Bailey says. "I'm
sure we'll find more and more drugs that are affected
this way."
To
date, grapefruit, orange and apple juices have been
shown to lower the absorption of etoposide, an
anticancer agent; certain beta blockers (atenolol,
celiprolol, talinolol) used to treat high blood pressure
and prevent heart attacks; cyclosporine, a drug taken to
prevent rejection of transplanted organs; and certain
antibiotics (ciprofloxacin, levofloxacin, itraconazole).
But additional drugs are likely to be added to the list
as physicians become more aware of this drug-lowering
interaction, Bailey says.
Orange and apple juices also appear to contain naringin-like
substances that inhibit OATP1A2, Bailey says. The
chemical in oranges appears to be hesperidin, but the
chemical in apples has not yet been identified, the
researchers notes.
Bailey advises patients to consult with their doctor or
pharmacist before taking any medications with grapefruit
juice or other fruits and juices. Unless it is known to
be a problem, he recommends taking most medications only
with water. This research was funded by grants from the
Canadian Institutes of Health Research and the United
States Public Health Service.
|
|
All rights reserved