Objectives: This research aimed to examine associations between patients’ non-adherence to their prescribed immunosuppressant medication and hospitalization outcomes. Primary endpoints included inpatient costs and length of stay (LOS) in the hospital. Both endpoints were measured as continuous variables.

Methods: For the calendar year 2019, adult patients, aged 18-65, who take immunosuppressants, and have at least one inpatient hospital stay, were identified in the Marketscan database. Those who were not continuously enrolled in their healthcare plan for the year were excluded from this study. Also, this study is limited to those admitted for medical (n=2056) or surgical (n=1352) care. Patients are considered adherent using proportion of days covered (PDC) metric if they have medicine on hand for at least 80% of the days in the year. Both inpatient costs and LOS were modeled as a function of the patients’ adherence status and controlling for the type of hospital admission.

Results: Overall, 2354 out of the 3408 (69%) were adherent. Of the medical admissions, 1366 (66%) were adherent. Among the surgical admissions, 988 (73%) were adherent. The patients’ gender, age, and region of the country have no significant impact on inpatient costs. On average, the adherent group of patients had LOS 2.5 (p<.0001) days shorter than the non-adherent group. Also, the adherent group had lower inpatient costs of $8214 (p=.038), when controlling for the admission type.

Conclusions: The lower costs and shorter stays of the adherent group indicates that interventions to increase drug adherence could help achieve the Triple Aim of lowering costs, improving quality care, and improving patient experience. Future research should examine which interventions are most effective for in improving patient adherence.