In article <1103[email protected]
"zwalanga" <[email protected]
> I have just had a conversation with the study author. In response to my
> query about alcohol consumption in one who cannot tolerate or take
> alcohol, he suggests grapefruit and/or grapefruit juice.
> Dr. Franco will be reading here today.
Something to investigate.
Grapefruit Juice and Medications: A Potential for Adverse Events
Many patients may take their medications with a glass of juice. However,
since the accidental discovery of an interaction between the calcium
channel blocker, felodipine, with grapefruit juice,1 it has now become
evident that grapefruit juice has the potential to
alter the plasma concentrations of many medications when they are taken
by mouth. In some cases, this may result in undesirable clinical effects
Administration of grapefruit juice in humans results in a decrease in
the level of CYP3A in the intestine,2 an important site for metabolism
for many medications. This mechanism would account for the increase in
levels of medications that are metabolized by CYP3A when concomitantly
administered with grapefruit juice.
A list of medications that have been shown, in clinical studies, to have
an interaction with grapefruit juice can be found in the table below.
All of the medications, except for theophylline and itraconazole, are
known to be substrates of CYP3A. When given with grapefruit juice in
pharmacokinetic studies their availability increases. In most cases, the
clinical consequence of the pharmacokinetic interaction has not been
evaluated. However, for midazolam and triazolam, as well as for
buspirone, impairment of CNS function was observed, and for the calcium
channel blocker felodipine greater blood pressure lowering has been
observed. In contrast to the increased levels of the other medications,
the grapefruit juice interaction observed with theophylline and
itraconazole was reduced plasma concentrations. The mechanism for this
effect has not been determined.
Although the clinical consequence of the grapefruit juice interaction
with most of the listed drugs has not been evaluated, increased plasma
concentrations of many of these drugs could result in adverse outcomes.
Examples include excessive lowering of blood pressure with the calcium
channel blockers, rhabdomyolysis and the potential for renal impairment
with the HMG CoA reductase inhibitors, and adverse pulmonary effects of
amiodarone. Inconsistent use of grapefruit juice or variability in its
effect on drug metabolism could result in variable and difficult to
control plasma concentrations of other medications, where maintaining a
certain plasma concentration may be especially important, such as for
cyclosporine or for HIV protease inhibitors like saquinavir.
In light of the potential for serious adverse outcomes, patients taking
medications with a potential for interaction with grapefruit juice
should be advised to avoid drinking grapefruit juice. Possible
interactions with whole grapefruit have not been evaluated but it would
be assumed to have similar effects.
Drug Class (Therapeutic Uses)
Antihypertensive (high blood pressure)
Not available in the United States
Antilipemic (lowers cholesterol)
Antimalarial (malaria infection)
Antiretroviral (HIV infection)
Anxiolytic (anxiety); Sedative (sleep)
Bronchodilator (asthma, bronchospam)
Theo-Dur, Slo-bid, others
GI stimulant (stimulates GI motility)
Estrogen (birth control, hormone replacement therapy)
Ortho-Novum, Loestrin, femhrt, others
Immune suppressant (prevents organ rejection)
Neoral, Sandimmune, SangCya
Antifungal (fungal infection)
Antiarryhthmic (heart rhythm)
Note: Medication names are hyperlinked to references in PubMed
1. Bailey DG, Spence JD, Munoz C, Arnold JMO.
Interaction of citrus juices with felodipine and nifedipine. Lancet
2. Lown KS, Bailey DG, Fontana RJ, et al.
Grapefruit juice increases felodipine oral availability in humans by
decreasing intestinal CYP3A protein expression.
Return to Drug Interaction Advisory Index
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