Background/Purpose:   Immunosuppressive and antimalarial drugs improve outcomes in systemic lupus erythematosus (SLE), including reducing disease activity, damage and mortality.  Although prior studies have found low adherence to medications in SLE, little information is available on the impact of adherence on health utilization and outcomes.   In this study, we examined whether poor adherence is associated with higher acute care utilization in a nationwide study of Medicaid beneficiaries.

Methods: We used 2000-2006 U.S. Medicaid Analytic eXtract (MAX) data containing person-level files on Medicaid eligibility, utilization and payments.  We identified patients with at least two years of continuous enrollment, who met an administrative definition of SLE and had received either an immunosuppressive (cyclophosphamide, mycophenolate, mycophenolic acid, azathioprine, leflunomide, methotrexate, or tacrolimus) or antimalarial (hydroxychloroquine) drug through an outpatient pharmacy.  Pharmacy claims were used to assess adherence by calculating a medication possession ratio (MPR) in the 1st year (“baseline year”), defined as the proportion of days covered by the total days’ supply dispensed after the first claim for each drug.  Average MPR for SLE drugs in the baseline year was used to examine outcomes in a subsequent one-year period (“follow-up year”).  Outcomes included all cause hospitalizations, SLE-related hospitalizations and emergency room (ER) visits.  We used Poisson regression models to evaluate the impact of low adherence (average MPR<80%) on utilization outcomes in the follow-up year, adjusting for baseline age, sex, race/ethnicity, Charlson comorbidity index, SLE-specific risk index (Ward M, J Rheum, 2000) and number of SLE drugs taken.

Results: 15,955 patients with SLE were taking at least one immunosuppressive or anti-malarial drug and continuously enrolled in Medicaid over the two-year period.  Mean age was 38.6 years (SD 11.3), 95% were female, and 39% were Black, 34% White, 16% Hispanic, 5% Asian, 5% other, 1% Native.   The average MPR during the baseline year was 49% (SD 30%).  In the follow-up year, 28% had one or more hospitalizations, 17% SLE-related hospitalizations, and 49% ER visits.   Lower adherence was associated with significantly increased risks of subsequent hospitalizations and ER visits, even after adjustment for sociodemographic factors, SLE risk index, comorbid disease, and number of SLE drugs taken (Table).

Conclusion:   We found that lower adherence (MPR<80%) significantly increased risks of subsequent hospitalizations and ER visits in Medicaid beneficiaries with SLE.  These results are consistent with past studies highlighting the importance of promoting medication adherence to improve health outcomes and decrease costs. Further research is warranted to gain a better understanding of how disease activity and severity influence this relationship.