This weeks
Question:
It's okay to take statin’s and other drugs that interact with
grapefruit, as long as they are separated by two hours.
1. True
2. False
Patients often ask how long to avoid grapefruit juice if they take
certain drugs.
Some are being told to avoid grapefruit altogether...others are told
to separate grapefruit from their drugs by a few hours.
Grapefruit can increase the levels of many drugs...lovastatin, simvastatin,
diazepam, some calcium channel blockers, protease inhibitors, etc. Certain
substances in grapefruit inactivate CYP3A4 in the gut.
Now there's evidence it can take THREE DAYS or LONGER for enzyme activity
to recover.
New evidence is also surfacing that suggests other fruits can have effects
similar to grapefruit...tangelos...limes...and Seville oranges. But
there's no interaction with most other citrus fruits...sweet oranges...
lemons...tangerines...and citrons.
In addition to grapefruit juice, keep in mind that the fruit itself
can be a problem. Most of the studies indicate that 8 ounces of grapefruit
juice is enough to cause the interaction. Just one small glass of grapefruit
juice occasionally is not likely to be a problem. But to be safe, tell
patients to avoid grapefruit entirely if they're taking meds that interact.
Explain that separating grapefruit from their meds by a few hours won't
decrease the possibility of an interaction.
References:
Kehoe WA. Timing of grapefruit juice drug interactions. Pharmacist's
Letter 2000;16:161008.
Bailey D, Malcolm J, Arnold O, et al. Grapefruit juice-drug interactions.
Br J Clin Pharmacol 1998;46:101-10.
Levien T, Baker D. Selected interactions caused by cytochrome P-450
enzymes. Pharmacist's Letter 1999;15:150401.
Fuhr U. Drug interactions with grapefruit juice. Extent, probably mechanism
and clinical relevance. Drug Safety 1998;18:251-72.
Fukuda K, Guo L, Ohashi N, et al. Amounts and variation in grapefruit
juice of the main components causing grapefruit-drug interaction. J
Chromatog B 2000;195-203.
Takanaga H, Ohnishi A, Murakami H, et al. Relationship between time
after intake of grapefruit juice and the effect on pharmacokinetics
and pharmacodynamics of nisoldipine in healthy subjects. Clin Pharmacol
Ther 2000;67:201-14.
Lundahl J, Regardh C, Johansson G. The interaction effect of grapefruit
juice is maximal after the first glass. Eur J Clin Pharmacol 1998;54:75-81.
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