This study updated a 2001 decision economic model that used indirect data and confirmed its findings by developing a new cost-effectiveness model by using now available head-to-head data. The models compared olanzapine with ziprasidone in the treatment of schizophrenia in the United States.
A decision analytic modeling approach was used to estimate annual health-care costs and health outcomes, incorporating events such as response, relapse, and suicide. Patients without response to first-line treatment switched to the other comparator. Decision tree probabilities were extracted from head-to-head studies and other published clinical literature. Direct health-care costs and quality-adjusted life-years (QALYs) were estimated on the basis of resource use and utility weights for initial and relapse episodes, maintenance therapy, and extended episodes of illness. Disutilities associated with treatment-emergent adverse events were included.
Consistent with the 2001 model, this model found that first-line treatment with olanzapine is associated with fewer hospital days, fewer days with extrapyramidal symptoms, and higher QALYs than is first-line treatment with ziprasidone. Total costs were lower for the olanzapine pathway ($70,232–$72,776 vs. $73,086–$73,310 in the Positive and Negative Syndrome Scale analysis) due to the cost savings associated with reduced health-care resource use. The incremental cost per QALY gained indicated that the olanzapine pathway dominated the ziprasidone pathway.
Decision analytic models should be continuously assessed against new data. This case study shows that incorporating new data confirmed results of a previously published model in which olanzapine was associated with better expected health outcomes and lower total health-care costs than was ziprasidone.