Psycho-Babble Medication Thread 34667

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Grapefruit Interactions/calcium interactions

Posted by Susan the Crone on May 25, 2000, at 18:51:47

I've read recently about NOT taking pills with grapefruit juice, and
even about avoiding grapefruit juice/grapefruit entirely because of interations
with some drugs.

AND, I've also read that either Effexor XR or Neurontin should not be taken
at the same time/possibly interact with calcium -- and I take Tums every day.

Any info on interactions??
Thanks!

Re: Grapefruit Interactions/calcium interactions

Posted by Cam W. on May 25, 2000, at 23:52:08

In reply to Grapefruit Interactions/calcium interactions, posted by Susan the Crone on May 25, 2000, at 18:51:47

Susan - Grapefruit juice contains 2 compounds that inhibit the a liver enzyme system called the cytochrome P450 system (specifically CYP-3A3/4). This enzyme system metabolizes many drugs (eg calcium channel blockers, many antidepressants, some antisychoticss, some benzodiazepines, non-sedating antihistamines, some anti-AIDs drugs, ethinylestradiol (BC pill), Prepulsid, and some others.

By inhibiting the CYP-3A3/4 system the concentrations of the above drugs "can" increase in the bloodstream due to a decrease in their metabolism. Usually, large amounts of grapefruit juice are needed for this to happen.

The chemicals in grapefruit juice that they think are responsible for this are 3,4-bergamottin (sp?) and, to a lesser extent, naringenin.

As for calcium, some divalent cations (like calium, magnesium, iron, etc) can bind to certain drugs and prevent their absorption (eg tetracycline). Also, calcium can act as an antacid, modifying the pH of your intestine and affecting the absorption of some drugs.

Neurontin's absorption is decreased by about 1/4 when taken with aluminum and magnesium-based antacids (eg Maalox). I am not sure if calcium also does this.

I have not heard of Effexor's absorption being modified by calcium.

Hope this helps - Cam

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