N-DESMETHYLCLOZAPINE, AN INSENSITIVE MARKER OF CLOZAPINE-INDUCED AGRANULOCYTOSIS AND GRANULOCYTOPENIA

We reviewed the charts of 58 patients with treatment-refractory schizo phrenia who were receiving clozapine, to determine if the drug's activ e metabolite, N-desmethylclozapine, is a biologic marker for impending clozapine-induced granulocytopenia and agranulocytosis. No significan t correlation between granulocyte counts and patient demographic varia bles of clozapine and N-desmethylclozapine steady-state plasma concent rations, clozapine:N-desmethylclozapine ratio, age, gender, clozapine dosage, smoking status, and race were found. We believe N-desmethylclo zapine is not a clinically useful marker for monitoring the effect of clozapine on granulocyte integrity. On the contrary, its plasma concen trations correlated positively with granulocyte counts.