Clozapine dose in the United States and Europe: implications for therapeutic and adverse effects.

The report (1) provides an overview of clozapine doses used in trials conducted in Europe and the United States, (2) compares data on efficacy, and (3) compares side effects of clozapine from recent European and U.S. investigations. The reviewed European trials used a mean dose of 283.7 mg/day, while the mean dose in the U.S. studies was 444 mg/day. Even though the mean doses used in the United States are considerably higher than those used in Europe, the response rates for the two continents are strikingly similar. The main differences in a comparison of two samples evaluated in New York and Innsbruck were found in the prevalence of seizures (Innsbruck, 0%; United States, 7.1%) and confusion (Innsbruck, 0%; United States, 14%). Excitement was less prevalent in the U.S. study. The data presented appear to suggest that a lower dose of clozapine may be as effective as a higher dose in the management of treatment-resistant schizophrenic patients and may cause fewer side effects.