Aims: This study explored the association between medication adherence to oral atypical antipsychotics (AAP) and both psychiatric hospitalization and associated costs in bipolar I disorder (BD-I) in a real-world setting.
Materials and methods: This retrospective study used the Truven Health MarketScan Medicaid, Commercial, and Medicare Supplemental Claims Databases. Adults were identified if they had BD-I and initiated an AAP treatment during the study identification period (July 1, 2015-June 30, 2016 for Medicaid, July 1, 2015-March 31, 2016 for Commercial and Medicare Supplemental) and had ≥6-month continuous enrollment before (baseline) and after (follow-up) the first day of treatment. Medication adherence was measured by the proportion of days covered (PDC) and grouped as: fully-adherent (PDC ≥80%), partially-adherent (40% ≤ PDC <80%), and non-adherent (PDC <40%). Logistic and linear regression models were conducted to estimate the risk of psychiatric hospitalization and costs during the 6-month follow-up period.
Results: The final sample consisted of 5,892 (32.0%) fully-adherent, 4,246 (23.1%) partially-adherent, and 8,250 (44.9%) non-adherent patients. The adjusted rate of psychiatric hospitalization during the follow-up period was lower in the fully-adherent (6.0%) vs partially- (8.3%) or non-adherent (8.8%) groups (p < 0.001). Using the fully-adherent cohort as the reference group, the odds of psychiatric hospitalization were significantly higher for the partially-adherent (OR = 1.42; 95% CI = 1.23-1.64) and non-adherent (1.51; 1.33-1.71) cohorts. The mean adjusted psychiatric hospitalization cost over 6 months among hospitalized patients was lower for the fully-adherent cohort ($11,748), than the partially-adherent ($15,051 p = 0.002) or non-adherent cohorts ($13,170, not statistically significant).
Limitations: The medication adherence measures relied on prescription claims data, not actual use.
Conclusions: In the treatment of BD-I, better medication adherence to AAP was associated with fewer psychiatric hospitalizations. Among hospitalized patients, fully-adherent patients had statistically significantly lower psychiatric costs than partially-adherent ones. These findings suggest that improving adherence to AAP in BD-I may be a valuable goal from both clinical and economic perspectives.
Keywords: Atypical antipsychotics; I15; I19; bipolar I disorder; cost; medication adherence; psychiatric hospitalization.