Assessment of the impact of second-generation antipscyhotics in Medi-Cal patients with bipolar disorder using panel data fixed effect models

Unrestricted While the comparative efficacy of second-generation antipsychotics (SGAs) vs. first generation antipsychotics (FGAs) has been well documented, the treatment effect of SGAs in bipolar disorder has not been directly evaluated in a real-world setting. Panel data fixed effects models provide a simple yet powerful tool in measuring treatment effects. The objectives of this study were to investigate the treatment effect of SGAs in bipolar patients enrolled in the fee-for-service (FFS) Medi-Cal program using panel data fixed effect models. The retrospective paid claims files from the Medi-Cal program was used. Patients were included if they had at least 1) one claim(s) for any bipolar medications and 2) one medical claim(s) with ICD-9 codes 296.40-296.99. The population was further defined as: 1) patients who initiated a new antipsychotic therapy between 2000 and 2001 (index date); 2) were 18 ≤ age at the index date; and 3) were continuously eligible for Medi-Cal during the 2-year pre- and post-index date period. Fixed effects panel data linear models were fitted for continuous treatment outcomes while fixed effects Poisson regression models were used for count variables. The results show that compared to FGAs, SGA use was associated with a significantly larger increase in total healthcare costs (2366.0, p=0.028) as well as pharmacy costs (770.9, p <0.0001). The SGA group also had a larger increase in medical costs compared to the FGA group (1687.0, p=0.09). These results suggest that the anticipated improvements in medical utilizations for the SGAs-treated patients were not realized resulting in a greater increase in healthcare costs in the SGA group. The results form the fixed effect Poisson analyses were consistent with this conclusion, indicating that SGA use did not have significantly positive impact on the utilization of the medical services examined.; When 3 SGAs were compared head-to-head, there was no significant difference in outcomes between patients treated with olanzapine and risperidone. The quetiapine group had a significantly lower pharmacy costs compared to the olanzapine group. However, the savings in pharmacy costs did not translate into savings in the total healthcare costs primarily due to the increase in medical costs in the quetiapine group.