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Caffeine interacts with some psychoactive meds. (Be Alert for Adverse Reactions).

TUCSON, ARIZ. -- Caffeine interacts with a number of psychoactive medications, and physicians must be alert to potentially serious consequences, Marilyn R. Semenchuk, Pharm.D., said at a psychopharmacology conference sponsored by the University of Arizona.

"We need to pay more critical attention to the amount of caffeine patients are consuming in their diets because it can be the source of adverse reactions," noted Dr. Semenchuk, who is CNS Regional Medical Scientist at GlaxoSmithKline in Tucson.

There are two potential sources of problems. In the first, phenothiazines and butyrophenones may form insoluble precipitates when given concurrently with caffeine. This can limit their absorption and overall effectiveness.

The other potential source of problems lies with the fact that caffeine is metabolized by the 1A2 isoenzyme of cytochrome P450.

Fluvoxamine causes a high degree of inhibition of this isoenzyme, which can also be inhibited by high doses of paroxetine, fluoxetine, and sertraline. The effect is to increase the half-life of caffeine from 5 hours to as long as 31 hours. This may result in insomnia, anxiety irritability and tremor.

Dr. Semenchuk said that this reaction can often go unnoticed, or it may be attributed to the fluvoxamine itself and not to caffeine.

In another example of a caffeine interaction, Dr. Semenchuk described the case of a patient who drank 5-10 cups of coffee daily.

Shortly after being switched to clozapine from another antipsychotic, he noticed that he would have brief psychotic episodes a few hours after taking clozapine with his coffee. This did not happen when he took clozapine with noncaffeinated beverages.

Dr. Semenchuk advanced two possible mechanisms for this effect. It's possible that clozapine formed an insoluble precipitate in the presence of caffeine and was not absorbed.

Alternatively, since clozapine is also metabolized by the 1A2 isoenzyme of cytochrome P450, some kind of competitive inhibition may have been involved.

Other medications that are metabolized by this isoenzyme include haloperidol, olanzapine, thioridazine, tacrine, amitriptyline, imipramine, clomipramine, warfarin, propranolol, methadone, verapamil, and theophylline, Dr. Semenchuk said at the conference.
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Author:Finn, Robert
Publication:Clinical Psychiatry News
Article Type:Brief Article
Date:Apr 1, 2002
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