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Old 04-24-2004, 11:42 PM
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Why can't you have grapefruit when taking Xanax?

I recently started taking Xanax and on the bottle it has a warning that says not to eat grapefruit or drink grapefruit juice while taking this medicie...why is that?
Old 04-25-2004, 12:00 AM
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I'm not sure about the specfic chemical details, but there's a substance in grapefruit that ramps up the effects of the Xanax.

I actually used to wash down Xanax with grapefruit juice...

not something I'd recommend, I'm just saying, is all...
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Old 04-25-2004, 12:07 AM
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Grapefruit juice can have drastic effects on the absorption of some medications:

http://psa-rising.com/eatingwell/citrus_effects.html

http://psa-rising.com/eatingwell/citrus_effects.html

http://somersetmedicalcenter.com/18448.cfm

http://edis.ifas.ufl.edu/BODY_FS088

...as you can see, it's not just Xanax.
Old 04-25-2004, 12:12 AM
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It's not at all specific to Xanax.

Grapefruit juice interacts with numerous drugs (and increases their blood concentrations by a variety of mechanisms).

Here is a concise chart showing some of the interactions.
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Old 04-25-2004, 12:13 AM
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That was actually a simul-post. Sorry.
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Old 04-25-2004, 01:00 AM
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Interesting. I took Xanax almost daily for nearly 2 years and never got one of these warnings on my bottles.
Old 04-25-2004, 07:19 AM
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It has to do with metabolic enzymes... grapefruit juice inhibits cytochrome P450 expression, which can increase the effect of some medications.

The labeling on Xanax is fairly new.
Old 04-25-2004, 10:32 PM
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i've read about this phenomenon, and i've had this question: instead of telling people to avoid grapefruit juice with their medication, why not give them a lower dose of medicine and tell them to take it with grapefruit juice? in general, isn't it healthiest to take the lowest effective dose of a medication?
Old 04-25-2004, 10:36 PM
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Well, I know the pharm. compananies love to offer their meds in comically-large doses, so that they're more marketable. The reasoning is that if one guy responds well to 5 mg. but the next guy needs 25, making the lowest available dosage 75 mg. ensures that it's enough for everyone.

Of course, this is ridiculous, as higher mg's all but guarantee more (bad, undesriable) side effects, and the vast majority (something like 80%+) of people respond well to much lower doses than are available.
Old 04-25-2004, 10:48 PM
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In theory you could do that but it's frought with danger insofar as there is no standard amount/potency of grapefruit, whereas there is a standard, a very well defined one, of medication. Rather than risk the uncertainties of various types/sizes/origins of grapefruit, why not just avoid it altogether?

And, although it's true you want to use the lowest effective dose of a drug, that's because you generally want the lowest effective blood level of that drug. If you wind up with the same blood level by either a) giving a higher dose and no grapefruit or b) a lower dose but with grapefruit, and the latter runs the risks associated with non-standardization, what's the gain?

One way your idea could be justified is if the medicine was very expensive so that it paid to screw up the drug's breakdown/clearance in order to use a lower dose of it (and save money). That was done here (with ketoconazole playing the role of grapefruit).
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Old 04-25-2004, 11:17 PM
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Quote:
Originally Posted by KarlGauss
In theory you could do that but it's frought with danger insofar as there is no standard amount/potency of grapefruit...
Plus there's person to person variation in the amount of cytchrome p450-3A4 (and other affected p450s) in liver tissue, and differences in the extent to which inhibitors induce production of more p450. When the drug is cheap, there's no good reason to open up a big old can of worms in order to minimize the effective dose.
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