ICI 204,636, an Atypical Antipsychotic

ICI 204,636 is a new, potentially atypical antipsychotic. In early phase II trials, the antipsychotic was well tolerated and results suggested efficacy in the treatment of the positive and negative symptoms of schizophrenia. The efficacy and safety of ICI 204,636 were evaluated on a larger scale in a 6-week, multicenter, double-blind trial. Hospitalized patients who met DSM-III-R criteria for chronic or subchronic schizophrenia with acute exacerbation, as well as other criteria, were randomized to ICI 204,636 (75 to 750 mg daily) (N = 54) or placebo (N = 55). Patients were assessed weekly by use of the Brief Psychiatric Rating Scale (BPRS), Scale for the Assessment of Negative Symptoms (SANS), and Clinical Global Impression Scale (CGI) for efficacy and the Simpson Scale and Abnormal Involuntary Movement Scale for extrapyramidal side effects (EPS). Significant differences (p < or = 0.05) between treatment groups, which favored ICI 204,636, were identified throughout the trial. Endpoint differences were significant (by analysis of covariance) for BPRS factor IV (activation) and SANS scores and were marginally significant for total BPRS, BPRS factor III (thought disturbance), BPRS positive-symptom cluster, and CGI Severity of Illness item scores (p = 0.07, 0.09, 0.06, and 0.09, respectively). ICI 204,636 was well tolerated, although it was associated with mild transient increases in alanine aminotransferase and a higher incidence of somnolence and anticholinergic effects compared with placebo. In the dose range studied, treatment with ICI 204,636 did not induce EPS as determined by analysis of Simpson Scale total scores and lack of treatment-emergent acute dystonic reactions. Furthermore, ICI 204,636 did not produce sustained levels of prolactin; the mean change from baseline at endpoint (-7.2 micrograms/L) was comparable (p = 0.44) to that for placebo (-8.2 micrograms/L). These findings distinguish ICI 204,636 from standard antipsychotics and confirm preclinical predictions that ICI 204,636 is an atypical antipsychotic.