Differential use of extended and immediate release quetiapine: a retrospective registry study of Finnish inpatients with schizophrenia spectrum and bipolar disorders

OBJECTIVE Extended release (XR) and immediate release (IR) quetiapine have differing dosing, titration and plasma concentration profiles. The authors assessed whether the use of quetiapine XR and IR in schizophrenia spectrum disorders (SCZ) and bipolar disorder (BD) differ. DESIGN Retrospective non-interventional registry study. SETTING Secondary healthcare. PARTICIPANTS All SCZ and BD (ICD-10 codes F20-F29, F30-F31) patients discharged between June 2008 and June 2010 from a Finnish psychiatric hospital with any use of quetiapine during their inpatient stay. PRIMARY AND SECONDARY OUTCOME MEASURES Differences in patient characteristics between quetiapine XR and IR users were tested. To assess the profile of XR versus IR patients, logistic regressions were performed. RESULTS 43 patients used quetiapine XR, 58 used quetiapine IR and 55 used both formulations (n=156). 102 patients were diagnosed with SCZ and 54 with BD, with no significant differences between the quetiapine formulations. The mean daily dose of quetiapine XR was significantly higher than that of quetiapine IR (542 mg vs 328 mg; p<0.001). This was also true for the SCZ subgroup (XR: 593 mg vs IR: 338 mg; p<0.001) and the BD subgroup (XR: 466 mg vs IR: 308 mg; p=0.009). 48% of all quetiapine IR patients used a mean dose of ≤200 mg compared with 2% of XR patients. Injectable antipsychotics were combined with quetiapine IR but not with quetiapine XR (12% vs 0%; p=0.019). At discharge, quetiapine XR was used as monotherapy to a greater extent than IR (79% vs 44%; p=0.003). The odds for quetiapine XR use in hospital were lower with advancing age, substance abuse diagnosis and prior IR use. CONCLUSIONS Among SCZ and BD inpatients, quetiapine XR was more often used as monotherapy and in significantly higher doses than quetiapine IR. Differential use of the quetiapine formulations appears to depend, at least in part, on patient characteristics.