Does independent nurse practitioner practice improve medication adherence and reduce costs?
Background: Scope of practice (SOP) regulations for nurse practitioners (NP) may be an important state policy tool in the delivery of primary care services. Currently 19 states have implemented legislation that allows NPs to practice and prescribe independently from physicians. Research suggests that states with independent SOP laws for NPs attract greater number of NPs, experience an increase in primary care visits, and have a decrease in ER admission rates. The extent to which these laws affect patient outcomes and prices is less clear. This study is the first to estimate the effect of independent SOP on a prescribing outcome, namely medication adherence.
Data: We used commercial health insurance claims from the Health Care Cost Institute (HCCI) over the years 2008 – 2012. Specifically, we used pharmacy claims to calculate patient-level annual medication adherence, measured as the proportion of covered days per year. Cost of care was calculated across the inpatient, outpatient, physician and pharmacy claims. The Area Resource File (ARF) provided state-level covariates such as income, unemployment rate and number of primary care physicians. We obtained data on number of NPs per state from the American Association of Colleges of Nursing to measure NP supply.
Methods: We employed a difference-in-difference regression to estimate the causal effect of SOP laws on medication adherence and costs of care. Medication adherence was measured for three cohorts of patients: those who received (1) antidiabetic, (2) antihypertensive, and (3) statin medications, based on a National Quality Forum approved measure that recommends these drug categories for measuring medication adherence. We estimated an ordinary least squares regression with controls for patient demographic and plan information, out-of-pocket share, state level covariates and patient fixed effects. Cost of care was examined using a generalized linear model. Separate regression analyses were conducted for each drug category patient cohort.
Results: We found no significant change in medication adherence when states introduced independent SOP for NPs. Annual total cost of care decreased significantly for states that switched to independent SOP for all three patient cohorts. Effects ranged from a $90 decrease among patients on antidiabetic medications (p<.01), to a $287 decrease among patients with antihypertensive medications (p<.0001), to a $600 decrease among patients who used statins (p<.0001).
Conclusions: Patient adherence for three major therapeutic categories remained unchanged after the implementation of independent SOP. Total cost of care decreased substantially across all three patient groups. Future research should examine whether the cost decrease is associated with changes in prescribing patterns or other differences in care provision. As states redesign the delivery of primary care services towards the goal of achieving efficient, high-quality care, the cost savings from independent SOP for NPs could serve as important evidence for states to move towards implementing independent SOP.