Question 197

Question:

A 25-year-old man is started on clozapine for schizophrenia, paranoid type. He had been unsuccessfully treated for the past 2 months with haloperidol. The patient should be monitored for which of the following adverse effects?

Correct Answer: B.  Decreased leukocyte count

Agranulocytosis (Answer B) is a rare adverse effect of all antipsychotics. The RBC (Answer A and E), platelet (Answer C) and eosinophil (Answer D) lines are not known to be affected by clozapine.
Clozapine is a (new-generation) atypical anti-psychotic that blocks 5-HT2 and dopamine receptors. Unlike the traditional antipsychotics, it is useful for treatment of the negative symptoms of schizophrenia. Its major side effect is agranulocytosis, which requires WBC monitoring.
Haloperidol is a high-potency dopamine blocker used to treat psychosis. Drugs in this class are more selective for dopamine receptors compared to low-potency antipsychotics such as chlorpromazine or thioridazine, hence haloperidol is the drug of choice to avoid cross-reactivity at muscarinic, adrenergic, and histaminic receptors. Long-term adverse effects of haloperidol include parkinsonian features and tardive dyskinesia secondary to blockade of the nigrostriatal pathway.