Elsevier

The American Journal of Medicine

Volume 124, Issue 11, November 2011, Pages 1081.e9-1081.e22
The American Journal of Medicine

AJM online
Clinical research study
Trouble Getting Started: Predictors of Primary Medication Nonadherence

Preliminary versions of this research were presented at the Society of General Internal Medicine annual meeting, April 29, 2010, Minneapolis, Minnesota, and the Academy Health Annual Research Meeting, June 28, 2010, Boston, Massachusetts.
https://doi.org/10.1016/j.amjmed.2011.05.028Get rights and content

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.

Section snippets

Data Sources

Data were obtained from 2 main sources: (1) iScribe, an e-prescribing system used in outpatient settings, and (2) a large pharmacy benefit management company. Both iScribe and the pharmacy benefit management company are owned and operated by CVS Caremark (Woonsocket, RI). During the study period, iScribe e-prescriptions were received by patients in all 50 states; the 8 states with the highest volume of iScribe use were New Jersey, New York, Tennessee, Florida, Texas, Maryland, South Carolina,

Results

A total of 3634 prescribers used the iScribe system during the 2008 calendar year. There were 280,081 patients who received iScribe e-prescriptions and filled at least 1 prescription claim. An additional 29,419 patients did not have any filled medication claims during the 2 years spanned by the claims data and thus were included only in secondary analyses.

A total of 1,147,701 e-prescriptions were written in 2008. Of these, 106,838 (9.3%) duplicates were excluded (7.2% reissued same day; 2.1%

Discussion

Medication nonadherence is common, but only with the recent advent of e-prescribing has the true extent of nonadherence become apparent. Our study adds to recent analyses documenting considerable nonadherence to e-prescribed medication.12, 13, 14, 15, 16 This larger and more nationally representative study confirms the high rates of nonadherence seen in other settings, finding that 24% of new e-prescriptions are not filled within 6 months. Most important, our present study identifies

Conclusions

This study adds to other recent analyses that demonstrate how common nonadherence is, but goes further by identifying factors that may be amenable to interventions to improve medication adherence. First, attention to formulary status and medication costs may promote adherence, although this will need to be tested further. Second, interventions aimed at addressing economic barriers to medication filling may help in addressing the income-based disparities in adherence that we observed. Finally,

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Funding: This work is supported by a research grant from CVS Caremark. Dr Shrank is supported by a career development award from the National Heart, Lung and Blood Institute (HL-090505).

Conflict of Interest: Dr Brennan, Dr Liberman, and Mr Hutchins are employees of CVS Caremark. Dr Schneeweiss has consultancies with WHISCON, RTI Health Solutions, and The Lewin Group. The remaining authors have no conflicts of interest to report.

Authorship: All authors had access to the data and played a role in writing this manuscript.

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