Impact of a transition to more restrictive drug formulary on therapy discontinuation and medication adherence

Abstract

What is known and objective: There is conclusive evidence demonstrating that formulary restrictions are associated with reduced utilization and pharmacy spending of the restricted drugs. However, prior efforts to implement restrictive formularies have been associated with inconsistent rates of therapy discontinuation and mixed impacts on adherence to therapy. Also, the impact of transferring patients from an already restrictive formulary to a more aggressive model has not been previously examined. This study evaluated the impact of implementation of a more restrictive formulary on therapy disruption, adherence rates, pharmacy costs and generic utilization among patients with common chronic conditions.

Methods: In 2014, CVS Health implemented Value Formulary (VF), a restrictive benefit design with the aim of reducing spending while preserving access to and adherence to essential therapy, was used. A retrospective cohort study was conducted to assess changes in therapy disruption rates, pharmacy costs and generic dispensing rate (GDR) (for continuers) and medication adherence (for initiators) following the implementation of VF. The study group was selected from members of three existing employer clients transitioned from standard formulary (SF) to VF on January 2014. The control population was a matched group of six employers with the same preperiod formulary structure, business unit, adherence programmes and patient out-of-pocket cost as the study group. The control group retained SF in 2014. To assess therapy disruption after VF implementation, we categorized patients by their subsequent medication use into three groups: (i) therapy stopped, (ii) therapy continued and (iii) therapy switched. Medication adherence was measured as monthly proportion of days covered (PDC). Pharmacy cost and GDR were measured per utilizer per month (PUPM). Rates of therapy disruption in study and control groups were compared using the chi-square test. Differences in monthly PDC between matched groups were evaluated using multivariate linear regression. Impact of VF on pharmacy cost and GDR was measured through segmented regression of interrupted time series data with generalized estimating equations.

Results and discussion: A transition from SF to VF influenced drug coverage for approximately 13% of members (as their medications were either no longer covered, or covered restrictively under VF). Compared to patients whose plan sponsors retained SF, the patients that transitioned to VF had a modest (1·3%) but statistically significant increase in therapy discontinuation rates. This was offset by similarly modest improvements in adherence; patients who initiated therapy under VF demonstrated a 1·5% higher adherence to medications as compared to SF patients (P < 0·001). Medication costs in the VF group were lower by $20 PUPM (P < 0·001), and GDR was greater by 4·2% (P < 0·001).

What is new and conclusion: Transition of patients to a more restrictive drug formulary led to modest therapy discontinuation, similarly modest improvements in medication adherence and substantial prescription drug cost savings. As healthcare payors search for ways to control the rapid rise in spending for medications without compromising quality, the Value Formulary can serve as a useful tool.

Keywords: drug formulary; drug utilization; generic utilization; medication adherence; pharmacy costs; restrictive formulary; therapy discontinuation; therapy disruption.