To examine the efficacy and tolerability of quetiapine SR in patients with schizophrenia switched from quetiapine IR.

Randomised, double-blind study (D1444C00146) using dual-matched placebo. Patients clinically stable on fixed doses of quetiapine IR received twice-daily quetiapine IR 400, 600 or 800 mg/day for 4 weeks. Stable patients were then randomised (1:2) to continue taking quetiapine IR or switch to the same total dose of quetiapine SR (active dose once-daily in the evening) for 6 weeks. Primary analysis: % of patients (modified ITT population) discontinuing due to lack of efficacy or with PANSS total increase ≥20% at any visit, using a 6% non-inferiority margin for the upper 95% CI of the treatment difference. Per-protocol (PP) analysis was also performed.

497 patients were randomised (quetiapine SR 331, IR 166); completion rates were 91.5% and 94.0%, respectively. Few patients discontinued due to lack of efficacy or had a PANSS increase ≥20% in both the MITT (n=496) and PP populations (n=393): 9.1% and 5.3% for quetiapine SR and 7.2% and 6.2% for quetiapine IR, respectively. Quetiapine SR was non-inferior to quetiapine IR in the PP population (treatment difference: -0.83% [95% CI -6.75, 3.71]; p=0017) but not in the MITT population (treatment difference: 1.86% [95% CI -3.78, 6.57]; p=0.0431). The incidence (quetiapine SR 38.7%; IR 35.5%) and profile of AEs were similar in both groups.

Clinically-stable patients receiving quetiapine IR can be switched, without titration, to an equivalent once-daily dose of quetiapine SR without any clinical deterioration or compromise in tolerability.