Effect of initial ziprasidone dose on treatment persistence in schizophrenia.

Objective: To determine the relationship between ziprasidone initial dose and treatment persistence among patients diagnosed with schizophrenia.

Method: Adult Medicaid recipients (N=1096) diagnosed with schizophrenia who had ziprasidone prescription claims between July 1, 2001 and September 30, 2003, were categorized by initial dose: low (20-60 mg per day, n=464), medium (61-119 mg per day, n=320) and high dose (120-160 mg per day, n=312). Treatment persistence up to 365 days was measured using refill patterns, allowing 15-day gaps between expected refill dates. Multivariate survival analysis explored the simultaneous impact of age, gender, race, previous hospitalization, and concomitant medication usage, in addition to initial dose of ziprasidone. Sensitivity analysis tested the robustness of results with different definitions for persistence and allowable gaps between refills.

Results: Discontinuation rates across the observation period (maximum, 12 months per individual) were lower for patients initiated with high-dose than low-dose ziprasidone (P=0.001). Other factors significantly associated with greater discontinuation of medication were monotherapy (versus combination therapy) and hospitalization within the 6 months prior to the index date of therapy. Black race was associated with greater discontinuation, although this was not consistent across sensitivity analyses.

Conclusions: Patients with schizophrenia started on high doses of ziprasidone have lower discontinuation rates in a retrospective Medicaid database than patients started on low doses. These results were robust across various sensitivity analyses.