Blood Clozapine Levels Elevated by Fluvoxamine: Potential for Side Effects and Lower Clozapine Dosage

Letter to the Editor

Sir: We report a case in which very high blood clozapine
levels occurred during concomitant use of fluvoxamine. Previous
reports have indicated that close monitoring should be done
when these two medications are coprescribed because of
fluvoxamine’s ability to inhibit hepatic microsomal enzymes
that metabolize clozapine. However, on the basis of this case
and the microsomal enzyme profiles of these two medications,
we believe that extreme caution is warranted.