Impact of real-world ziprasidone dosing on treatment discontinuation rates in patients with schizophrenia or bipolar disorder.

BACKGROUND: The purpose of this study is to evaluate the relationship between maximum dose of ziprasidone and time to discontinuation in the treatment of schizophrenia/schizoaffective disorder and bipolar disorder in clinical practice.

METHOD: The 2001-2006 MarketScan Commercial and Medicare Databases were analyzed for maximum ziprasidone doses achieved in patients with schizophrenia/schizoaffective disorder or bipolar disorder. Ziprasidone maximum-dose groups were defined as low (20-60 mg/d), medium (61-119 mg/d), or high (120-160 mg/d). Patients receiving >160 mg/d were excluded. Mean time to discontinuation was evaluated across propensity score-matched dosing groups. Cox proportional hazard models were used to adjust for confounding when comparing the high- and medium-dose groups with the low-dose group.

RESULTS: Data were available for 33,340 patients with schizophrenia/schizoaffective disorder, of whom 16.6% received low dose of ziprasidone, 22.0% medium dose, and 61.4% high dose. Of those subjects with bipolar disorder (n=27,751), 26.1% were receiving a low dose of ziprasidone, 25.7% a medium dose, and 48.3% a high dose. Among the propensity score-matched dosing groups, the respective mean time to discontinuation for low, medium, and high doses was 90.5, 117.2, and 201.6d within the schizophrenia/schizoaffective disorder cohort and 84.6, 110.7, and 173.2d within the bipolar cohort (p<0.0001 for all comparisons). The hazard ratios for discontinuing therapy were significantly lower for the medium- (0.84, 0.84) and high-dose (0.57, 0.60) groups relative to the low-dose group in schizophrenia/schizoaffective disorder and bipolar disorder, respectively.

CONCLUSIONS: Patients with schizophrenia/schizoaffective or bipolar disorders receiving ziprasidone 120-160 mg/d experienced a statistically significant lower discontinuation rate compared with those receiving lower doses.