Background/Purpose:   Immunosuppressive and anti-malarial drugs are the cornerstones of treatment for patients with systemic lupus erythematosus (SLE) and have been shown to improve outcomes, including reduced disease activity, damage and mortality.  We examined adherence to treatment with these medications in a nationwide study of Medicaid beneficiaries with SLE.

Methods: We used U.S. Medicaid Analytic eXtract (MAX) data from 2000-2006 containing person-level files on Medicaid eligibility, utilization and payments.  We identified patients meeting a validated administrative SLE definition, who had received either an immunosuppressive (oral cyclophosphamide, mycophenolate mofetil, mycophenolic acid, azathioprine, leflunomide, methotrexate, or tacrolimus) or anti-malarial (hydroxychloroquine) drug through an outpatient pharmacy over the period of observation.  Pharmacy claims were used to assess adherence to drugs by calculating a medication possession ratio (MPR), defined as the proportion of days covered by the total days’ supply dispensed after the first claim for each drug.  We observed each patient over a fixed interval of 180 days to ensure all patients were studied for the same time interval.  Data were stratified by sociodemographic characteristics and geographic region and we used Fisher’s exact test to compare MPRs between groups.  In addition, we examined the percentage of patients considered adherent, defined as having a MPR greater than or equal to 80%.

Results: 23,187 patients with SLE were taking at least one immunosuppressive or anti-malarial drug.  Mean age was 38 years (SD 12) and 94% were female.  The sample was diverse (40% Black, 34% White, 16% Hispanic, 5% Asian, 5% Other, and 1% Native).  Most resided in the U.S. South (36% vs. 18% Midwest, 23% Northeast, 22% West). MPRs ranged from 31.1% for tacrolimus to 56.9% for hydroxychloroquine (Table). Across all medications, Blacks had lower adherence compared to Whites.  For many medications, Asians had higher adherence than Whites.  For example, for hydroxychloroquine, the MPR was significantly higher among Asians (63, SD 27), and lower in Blacks (53, SD 29), Hispanics (57, SD 28), and Native populations (56, SD 26) compared to Whites (59, SD 31; p<0.0001 for group comparisons).  MPRs were lowest for patients residing in the Midwest, and highest for those in the Northeast (p<0.01 across drugs). A minority of patients had MPRs greater than or equal to 80% (range 14% for tacrolimus to 40% for mycophenolate mofetil; Table).

Conclusion:   Our study demonstrates poor adherence to all classes of medications used to treat SLE among Medicaid beneficiaries.  Although adherence was low across all racial/ethnic groups and regions examined, it was particularly low among Blacks, Hispanics and Native populations, as well as for those residing in the Midwest.  These findings suggest that a majority of Medicaid beneficiaries may be at risk for inadequate clinical response because of poor adherence.