Validation of an economic model of paliperidone palmitate for chronic schizophrenia.

Objective: Model validation is important, but seldom applied in chronic schizophrenia. Validation consists of verifying the model itself for face validity (i.e., structure and inputs), cross-validation with other models assessing the same issue, and comparison with real-life outcomes. The primary purpose was to cross-validate a recent pharmacoeconomic model comparing long-acting injectable (LAI) antipsychotics for treating chronic schizophrenia in Sweden. The secondary purpose was to provide external validation.

Methods: The model of interest was a decision tree analysis with a 1-year time horizon with costs in 2011 Swedish kroner. Drugs analyzed included paliperidone palmitate (PP-LAI), olanzapine pamoate (OLZ-LAI), risperidone (RIS-LAI), haloperidol (HAL-LAI), and oral olanzapine (oral-OLZ). Embase and Medline were searched from 1990-2012 for models examining LAIs. Articles were retrieved, with data extracted for all drugs compared including: expected costs, rates of hospitalization, proportion of time not in relapse, and associated QALYs. Outcomes from the model of interest were compared with those from other articles; costs were projected to 2012 using the consumer price index.

Results: Twenty-six studies were used for validation; 14 of them provided evidence for cross-validation, 13 for external validation, and four for cost. In cross-validation, cost estimates varied -1.8% (range: -12.4-20.1%), hospitalizations 5.2% (-12.1-3.1%), stable disease 2.5% (-5.6-1.5%), QALYs 9.0% (4.3% after removing outliers). All estimates of clinical outcomes were within 15%. In external validation, hospitalization rates varied by 6.3% (-0.7-11.3%). The research was limited by data availability and validity of the original results.

Conclusion: Other models validated the outputs of our model very well.