Trouble getting started: predictors of primary medication nonadherence

Abstract

Background: Patient nonadherence to prescribed medication is common and limits the effectiveness of treatment for many conditions. Most adherence studies evaluate behavior only among patients who have filled a first prescription. The advent of electronic prescribing (e-prescribing) systems provides the opportunity to track initial prescriptions and identify nonadherence that may have previously been undetected.

Methods: We analyzed e-prescribing data and filled claims for all patients with CVS Caremark (Woonsocket, RI) drug coverage who received e-prescriptions from the iScribe e-prescribing system in calendar 2008. We matched e-prescriptions with filled claims by using data on the drug name, date of e-prescription, and date of filled claims, allowing up to 180 days for patients to fill e-prescriptions. We evaluated the rate of primary nonadherence to newly prescribed medications across multiple characteristics of patients, prescribers, and prescriptions and developed multivariable models to identify predictors of nonadherence.

Results: We identified 423,616 e-prescriptions for new medications, with 3634 prescribers and 280,081 patients. The primary nonadherence rate was 24.0%. Several factors were associated with nonadherence to e-prescriptions, including nonformulary status of medications (odds ratio [OR] 1.31 compared with preferred medications; 95% confidence interval [CI], 1.26-1.36; P<.001) and residence in a low-income ZIP code (OR 1.23 compared with high-income ZIP code; 95% CI, 1.17-1.30; P<.001) Nonadherence occurred less often when e-prescriptions were transmitted directly to the pharmacy rather than printed to give to patients (OR 0.54; 95% CI, 0.52-0.57; P<.001).

Conclusion: 24% of e-prescriptions for new medications were not filled. Our results suggest that interventions to address economic barriers and increase electronic integration in the healthcare system may be promising approaches to improve medication adherence.