Extended-Release Formulation and Medication Adherence
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Price School of Public Policy, University of Southern California, Los Angeles, CA, USA; 2USC School of Pharmacy, Los Angeles, CA, USA; 3USC Schaeffer Center for Health Policy & Economics, Los Angeles, CA, USA; 4Keck School of Medicine, Los Angeles, CA, USA.
J Gen Intern Med DOI: 10.1007/s11606-019-05275-1 © Society of General Internal Medicine 2019
INTRODUCTION
Suboptimal adherence to chronic medications undermines treatment effectiveness and costs the USA as much as $289 billion annually.1 Prescription of extended-release (XR) formulations may offer a partial solution, as past studies have found that XR formulations can improve adherence.2 However, the majority of past studies have analyzed adherence to XR formulations only in the context of specific medications and short-term time frames (< 1 year).3, 4 This study investigates the effects of XR on long-term (≥ 1 year) adherence across 15 chronic medications, as well as the influence of cost-sharing on XR usage.
METHODS
An IRB exempted this study. We identified patients treated with chronic medications from a 25% sample of Optum’s Clinformatics® claims from 2011 to 2013. Patients were between 18 and 64, had at least two fills of XR/non-XR formulations of a selected medication, initiated treatment at least 1 year before December 31, 2013, and remained continuously enrolled in the same insurance plan until December 31, 2013. Adherence to a given drug/ formulation was measured at the patient level via variable medication possession ratio (MPR), defined as the sum of days’ supply (regardless of dosage) from first to last prescription (inclusive) divided by the time between the last and first prescription dates plus last days’ supply, without truncation.5 Patients who took both formulations were excluded. In total, 15 medications were analyzed (Fig. 1). Selected medications had both XR and non-XR formulations as of
Prior Presentations None
December 31, 2010, were intended for long-term use and had at least 100 users of each formulation. To examine the effects of XR formulations, we performed linear regressions to determine adjusted MPR, controlling for age, race, income, education, geographic area of residence, the Charlson comorbidity index, number of drugs taken concurrently, and plan type. We also defined adherence as MPR > 0.85 and generated adjusted adherence rates using logistic regression with the same controls. We also studied patients who initiated treatment in 2011 and calculated two fixed MPRs (denominator = 365), one beginning from a patient’s first fill to 1 year after treatment initiation, and another for the second year after initiation, with excess days’ supply truncated.5 Finally, we calculated out-of-pocket costs and conducted linear regressions to analyze the relationship between proportion of XR users and difference in out-of-pocket cost between XR and non-XR across the medications. Average adjusted MPRs, adherence rates, and out-ofpocket costs were weighted by total days’ supply of medications. Analyses were conducted using Stata (version 14
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