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Effect of initial ziprasidone dose on length of therapy in schizophrenia.

Joyce AT, Harrison DJ, Loebel AD, Carter CT, Ollendorf DA

PharMetrics, Inc., 311 Arsenal Street, Watertown, MA 02472, USA. ajoyce@pharmetrics.com

OBJECTIVE: To examine the effects of initial ziprasidone dose on discontinuation rates, using retrospective integrated medical and pharmacy claims data. METHODS: Patients > or = 18 years with a diagnosis of schizophrenia or schizoaffective disorder and a ziprasidone claim between March 2001 and February 2003 who were continuously enrolled for at least six months before and three months after initiation of ziprasidone were included. They were stratified by initial daily dose (> or = 40 and < 80 mg [low] vs. > or = 80 and < 120 mg [medium] vs. 120-160 mg [high]). The six-month risk of discontinuation was examined using Cox proportional hazards models controlling for gender, psychiatric comorbidities, and pre-ziprasidone utilization of antipsychotics (atypical, conventional, none). RESULTS: The mean age of the sample (n=1058) was 38 years; 42% were male. The six-month risk of discontinuation was significantly lower in patients in the high-dose group as compared to the low-dose group (HR=0.737 for high-dose vs. low-dose, 95% CI=0.581, 0.935; P=0.012) and trended towards significance when comparing high-dose and medium-dose groups (HR=0.857 for high-dose vs. medium-dose, 95% CI=0.694, 1.059; P=0.153). CONCLUSIONS: Patients initiating ziprasidone therapy with an initial dose of at least 120 mg/day had better medication adherence compared to those initiating at lower doses. These findings confirm results seen in clinical trials suggesting improved efficacy and tolerability at higher ziprasidone doses.

Published 4 April 2006 in Schizophr Res, 83(2): 285-92.
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