Quetiapine. A me-too neuroleptic; no panacea

Quetiapine, a so-called atypical neuroleptic, is authorised in the European Union for use in the standard indications of neuroleptics. However, it is the only neuroleptic licensed for the treatment and prevention of depressive episodes in patients with bipolar disorder, and as add-on therapy for depressive episodes inadequately improved by an antidepressant. In patients with schizophrenia, the authors of two meta-analyses, one including 12 trials (3443 patients) and the other 21 trials (4101 patients), concluded that quetiapine was not clearly more effective than other conventional or atypical neuroleptics. In bipolar patients with manic episodes, the results of two trials suggest that quetiapine monotherapy is not more effective than haloperidol or lithium. Two placebo-controlled trials of add-on quetiapine therapy in patients receiving a mood stabiliser (lithium or divalproate sodium) yielded conflicting results. In bipolar patients with a depressive episode, the only available trial, versus placebo and versus paroxetine in 740 patients, failed to provide conclusive evidence. In two trials with controversial designs, in which quetiapine was added to a mood stabiliser in order to prevent new depressive or manic episodes in bipolar patients, quetiapine appeared to be more effective than placebo: about 15% to 20% more patients were stabilised on quetiapine than on placebo. There are no trials to show whether quetiapine is more effective in preventing manic episodes than a neuroleptic. In a trial including 1226 patients in whom quetiapine was effective during a first depressive or manic episode, quetiapine appeared to be more effective than lithium in preventing a depressive episode (relapse rate 8.9% versus 13.5%) but not a manic episode. These comparisons may be biased, however. Two placebo-controlled trials assessed quetiapine add-on therapy in patients in whom an antidepressant was inadequately effective. The conflicting results obtained in these two trials rule out drawing firm conclusions as to the efficacy of quetiapine. Overall, quetiapine has the adverse effect profile common to atypical neuroleptics. However, hypercholesterolaemia is more frequent than with risperidone, and both clinical trials and post-marketing data have shown that quetiapine carries a risk of hypothyroidism. Animal studies suggested a risk of cataracts, but this adverse effect has not yet been confirmed in humans. The risk of sudden cardiovascular death appears similar to that reported with other neuroleptics. A retrospective survey suggests that the consequences of acute overdose are more severe with quetiapine than with other neuroleptics. Quetiapine is metabolised by cytochrome P450 isoenzyme CYP3A4, creating a high risk of pharmacokinetic interactions. In practice, quetiapine has not been shown to provide a therapeutic advantage over other treatments, although additional trials in the prevention of depressive episodes are warranted in selected patients.