Quetiapine for schizophrenia

Quetiapine is a novel atypical antipsychotic with low propensity for movement disorder adverse effects. It is used for treatment of schizophrenia and other psychoses.

To determine the effects of quetiapine for schizophrenia in comparison to placebo, classical and other atypical antipsychotics.

Electronic searches of Biological Abstracts (1982-1997), CINAHL (1982-1997), the Cochrane Library (1998, Issue 1), the Cochrane Schizophrenia Group's Register of trials (1998), EMBASE (1980-1998), MEDLINE (1966-1998), PsycLIT (1974-1997), SocioFile (1974-1997) and many conference proceedings and hand searches of specific journals were undertaken. Zeneca Pharmaceuticals was contacted for information regarding unpublished trials.

All controlled trials where adults with schizophrenia or similar illnesses were randomised to quetiapine, placebo or other neuroleptic drugs and where clinically relevant outcomes were reported.

Citations and, where possible, abstracts were independently inspected by reviewers, papers ordered, re-inspected and quality assessed. Data were also independently extracted. For homogeneous dichotomous data the Peto odds ratio (OR), 95% confidence interval (CI) and, where appropriate, the number needed to treat (NNT) was calculated on an intention-to-treat basis.

Seven trials of short duration are included (31 reports) and seven are excluded (15 reports). Apart from that of 'leaving the study early', all other results may be prone to bias and should be viewed with caution since dropout rates are high (48-61%) in each arm of all studies. There are data suggesting less people allocated quetiapine leave the study early (53%) than those in the placebo group (61%) (OR 0.67 CI 0.48-0. 95). Data incorporating considerable assumptions about the many people who left early suggest that global state and psychotic symptoms - both positive and negative - may be more helped by quetiapine than placebo. Although some of these data reach statistical significance their clinical importance is difficult to interpret. While the incidences of extrapyramidal side effects are not different between quetiapine and placebo, side effects such as dizziness and dry mouth are more prevalent in the quetiapine treated group. High proportions of trial participants also leave when quetiapine is compared to chlorpromazine or haloperidol (57% by six weeks). Quetiapine is as potent as chlorpromazine and haloperidol as regards global and mental state but it may cause higher incidences of dry mouth and sleepiness. Extrapyramidal side effects are the same as those of chlorpromazine but may be less than haloperidol. High dose quetiapine is better than low dose quetiapine with regard to leaving the study early, and limited data suggest that the higher dose is also better at marginally improving global state (n = 1, OR 0.70, CI 0.50-0.99, NNT 11). There are no clear differences between high and low dose groups in respect of extrapyramidal side effects.

The high dropout rates are a large problem in interpreting any results other than 'leaving the study early' since about half the data were not available at the end of studies. Before quetiapine's use can be recommended, we need more large, well conducted trials that provide short, medium and long term outcomes relevant to carers and clinicians.