Quetiapine: a new atypical antipsychotic

Quetiapine has recently been approved for treatment of psychotic disorders. In short term (6 weeks) trials this atypical antipsychotic was shown to be as efficacious as the standard antipsychotics for the treatment of the positive symptoms of schizophrenia without causing any extrapyramidal symptoms or increase in the prolactin levels. Its efficacy for treating the negative symptoms was variable. Preliminary observations suggest its potential to improve the cognitive deficits of schizophrenia. It is metabolized by the p450 CYP 3A4 system with an estimated elimination half life of 6 hours. The optimal treatment is 300 mg to 400 mg/day in two to three divided oral doses. The most common side effects include dizziness, hypotension, somnolence and weight gain. Changes in the ECG, the thyroid hormone and hepatic enzymes levels appear to be clinically insignificant. Quetiapine interacts with phenytoin, carbamazepine, barbiturates, rifampin and glucocorticoids; and coadministration with these drugs may require dosage adjustment. Doses need not be adjusted when fluoxetine, imipramine, haloperidol and resperidone are coadministered. Quetiapine may enhance the effects of antihypertensive agents and may antagonize those of levodopa and dopamine. Long term efficacy of quetiapine has not been determined. Also undetermined are its effectiveness for treating the first episode and treatment-refractory schizophrenia. Data suggest that quetiapine may be used for the management of psychotic disorders in patients who may not tolerate the side effects of the typical antipsychotics and clozapine. It may also be helpful in patients whose psychotic manifestations did not adequately respond to risperidone and olanzapine.