Cost-effectiveness of clozapine monitoring after the first 6 months

Clozapine is effective in treating patients with schizophrenia who do not respond to conventional neuroleptic drugs. The drug is unique in that it is available only with a US Food and Drug Administration-mandated system for weekly monitoring of patients' white blood cell counts. No study has been conducted to evaluate the cost-effectiveness of this mandatory monitoring system.

A benchmark case was established by utilizing cumulative incidence rates of agranulocytosis from a recent study with a large sample of clozapine-treated patients. We assumed a 20% mortality among patients with agranulocytosis, $30.61 in monitoring costs each week, and 14.4 years of remaining life expectancy after detection of agranulocytosis. Based on these bench-mark assumptions, cost-effectiveness ratios in dollars per quality-adjusted life-year were calculated for the first, second, and third 6-month periods during which a patient was receiving clozapine. Sensitivity analyses were performed with more conservative assumptions in 5 alternative scenarios.

In the benchmark case, costs per quality-adjusted life-year gained were $61,694, $925,418, and $420,644 for the first, second, and third 6-month periods of clozapine treatment, respectively. In the alternative scenarios, these costs ranged from $7923 to $46,056 for the first 6-month period and from $54,025 to $690,850 for the second and third 6-month periods.

While the costs of monitoring patients with schizophrenia in the first 6-month period of clozapine treatment seem to be justifiable, monitoring thereafter may not be cost-effective because of the very low incidence of agranulocytosis in the later periods.