Extrapyramidal side effects of clozapine and haloperidol.

Neuroleptic-induced extrapyramidal side effects (EPS) were evaluated in 92 patients treated with clozapine for the first time and 59 patients treated with haloperidol followed in a drug monitoring program. Side effects were measured by the Columbia University Rating Scale, the Simpson Dyskinesia Scale and the Hillside Akathisia Scale. The cumulative incidence rate for tremor was found to be 24.4% in the clozapine group and 39.3% in the haloperidol group. This did not amount to a statistically significant group difference. Bradykinesia was observed in 21.8% of the patients treated with clozapine and in 47.7% of the patients of haloperidol (P = 0.011). In the clozapine group the akathisia incidence rate was 5.6%, whereas haloperidol patients showed a higher rate of 31.7% (P = 0.005). Our results show higher incidence rates of tremor and bradykinesia during clozapine treatment than previous studies. We conclude that clozapine is not entirely free of EPS, but they are usually less severe and of a different quality than side effects induced by typical antipsychotics.