New prescription medication gaps: a comprehensive measure of adherence to new prescriptions

Abstract

Objective: Describe a novel approach to comprehensively summarize medication adherence.

Data sources/study setting: Kaiser Permanente Northern California Diabetes Registry (n approximately 220,000)

Study design: In a new prescription cohort design (27,329 subjects prescribed new medications), we used pharmacy utilization data to estimate adherence during 24 months follow-up. Proportion of time without sufficient medications (medication gaps) was estimated using a novel measure (New Prescription Medication Gaps [NPMG]) and compared with a traditional measure of adherence.

Data collection/extraction methods: Data derived from electronic medical records and survey responses.

Principal findings: Twenty-two percent of patients did not become ongoing users (had zero or only one dispensing of the new prescription). The proportion of newly prescribed patients that never became ongoing users was eightfold greater than the proportion who maintained ongoing use, but with inadequate adherence. Four percent of those with at least two dispensings discontinued therapy during the 24 months follow-up. NPMG was significantly associated with high out-of-pocket costs, self-reported adherence, and clinical response to therapy.

Conclusions: NPMG is a valid adherence measure. Findings also suggest a larger burden of inadequate adherence than previously thought. Public health efforts have traditionally focused on improving adherence in ongoing users; clearly more attention is needed to address nonpersistence in the very first stages after a new medication is prescribed.

Figure 1

Flowchart Depicting the 24-Month Observation Period for 27,329 Diabetic Patients Newly Prescribed a Single Cardiometabolic Therapy

Figure 2

Self-Reported Adherence (Days Missed out of Seven) for Cholesterol-Lowering Medications Relative to Adequate (<20 Percent Gap) versus Inadequate (≥20 Percent Gap) Adherence in New Prescription Medication Gaps (NPMG) and Continuous Medication Gaps (CMG). DISTANCE Study