Background. Quetiapine (ICI 204,636, ‘Seroquel’) is a new atypical antipsychotic agent with a
similar binding profile to the original atypical antipsychotic, clozapine. Its clinical efficacy has
already been demonstrated at multiple fixed doses (150–750 mg/day) and has been suggested to be
comparable with haloperidol (12 mg/day).
Methods. This international, 6-week, multicentre, double-blind, randomized, parallel-group trial
compared quetiapine with haloperidol (455 mg and 8 mg mean total daily doses, respectively) in 448
hospitalized patients with acute exacerbation of chronic or subchronic schizophrenia (DSM-III-R),
in order to establish their equivalence in terms of efficacy, and the nature of their tolerability
profiles, especially in terms of extrapyramidal symptoms (EPS) and serum prolactin levels.
Results. Both quetiapine and haloperidol produced a clear reduction in the Positive and Negative
Syndrome Scale (PANSS) scores and Clinical Global Impression (CGI) Severity of Illness and
Global Improvement scores. At day 42, the PANSS total score was reduced by −18·7±1·63 in the
quetiapine group, and −22·1±1·63 in the haloperidol group (P = 0·13, between-treatment).
Quetiapine was better tolerated than haloperidol in terms of EPS as demonstrated by the
significant differences in the Simpson Scale and Abnormal Involuntary Movement Scale scores
(P<0·05). Although patients in both groups had elevated serum prolactin concentrations at baseline,
mean serum prolactin concentration decreased (by 16·5 μg/l) in quetiapine-treated patients, yet
increased (by 5·9 μg/l) in patients treated with haloperidol.
Conclusion. Quetiapine is an effective and well tolerated antipsychotic of comparable efficacy to
haloperidol and lacks the latter compound's effect on prolactin and EPS.