We examined whether nonadherence to hydroxychloroquine (HCQ) or immunosuppressive medications (ISMs) was associated with higher subsequent acute care utilization among Medicaid beneficiaries with systemic lupus erythematosus (SLE).
We utilized US Medicaid data from 2000-2006 to identify adults ages 18-64 years with SLE who were new users of HCQ or ISMs. We defined the index date as receipt of HCQ or ISMs without use in the prior 6 months. We measured adherence using the medication possession ratio (MPR), the proportion of days covered by total days' supply dispensed, for the 1-year post-index date. Our outcomes were all-cause and SLE-related emergency department (ED) visits and hospitalizations in the subsequent year. We used multivariable Poisson regression models to examine the association between nonadherence (MPR <80%) and acute care utilization, adjusting for sociodemographics and comorbidities.
We identified 9,600 HCQ new users and 3,829 ISM new users with SLE. The mean ± SD MPR for HCQ was 47.8% ± 30.3% and for ISMs was 42.7% ± 30.7%. Seventy-nine percent of HCQ users and 83% of ISM users were nonadherent (MPR <80%). In multivariable models, among HCQ users, the incidence rate ratio (IRR) of ED visits was 1.55 (95% confidence interval [95% CI] 1.43-1.69) and the IRR of hospitalizations was 1.37 (95% CI 1.25-1.50), comparing nonadherers to adherers. For ISM users, the IRR of ED visits was 1.64 (95% CI 1.42-1.89) and of hospitalizations was 1.67 (95% CI 1.41-1.96) for nonadherers versus adherers.
In this cohort, nonadherence to HCQ and ISMs was common and was associated with significantly higher subsequent acute care utilization.