Dispensing Channel and Medication Adherence: Evidence Across 3 Therapy Classes
Published Online: October 22, 2013
Reethi Iyengar, PhD, MBA, MHM; Rochelle Henderson, PhD, MPA; Jay Visaria, PhD, MPH; and Sharon Glave Frazee, PhD, MPH
Medication adherence, defined as taking medications as prescribed, is a key component in controlling disease progression and managing chronic illnesses.1,2 The clinical benefits of medication adherence have been well established in the scientific literature. Previous studies have indicated that medication adherence is associated with reducing disease morbidity,3 reducing healthcare resource utilization,4 decreasing hospitalization,5 improving effectiveness of treatment,6 and increasing likelihood of survival.7
In addition to worse health outcomes, medication nonadherence is linked to increased healthcare costs. Nonadherence across just chronic therapy classes (antidiabetics, antihypertensives, and antihyperlipidemics) resulted in an estimated $105.8 billion in direct costs in the United States during 2010 alone.8 Nevertheless, this cost burden can be reduced. Previous studies have found that adherence rates of 80% or greater were associated with significant decreases in total medical costs for diabetes, hypertension, and high blood cholesterol.4
Studies have indicated that obtaining medication through the mail is one option for improved medication adherence.9-11 Compared with retail pharmacies, mail order has been touted as more cost-effective12 and convenient.13 In contrast, retail pharmacies are perceived to add value in terms of pharmacist face-to-face interaction.14-16 Proponents of mail order contend that medication adherence is greater among patients who secure medications via mail order, while proponents of retail attribute any improved adherence to the increased days of supply per prescription in mail order.14
Many patients who intend to take their medications as prescribed fail to get medications refilled due to various factors such as inability to visit a pharmacy, their schedule, forgetfulness, or procrastination. Mail order provides a convenient and effective alternative for continued access to medications. Inadequate access17 and financial concerns18 are 2 factors identified as impediments to adherence.19 The impact of access and cost is reduced for many patients by the use of mail order, because prescriptions are delivered to one’s home and the total patient out-of-pocket (OPP) costs are frequently less. Hence, we hypothesized that use of the mail order channel is associatedwith higher adherence rates than use of the retail channel.
A common limitation in adherence studies is the failure to control for underlying factors that affect adherence and selection of delivery channel. For example, it is quite possible that health-conscious individuals are more likely to have other healthy behaviors such as exercise, good diet, and preventive screenings. Hence, they may be more likely to engage proactively in activities that improve their adherence—sometimes referred to as the “healthy adherer” effect.20,21 Mail order generally provides more days of supply, regular refill reminders, and convenient reordering for members, mitigating the potential to procrastinate on medication refills, which can adversely affect adherence. Healthconscious individuals may choose the mail order channel to ensure continuity in their medication regimens. Thus, better medication adherence with mail order may reflect healthier patients’ predisposition to self-select the mail order option. To accurately attribute the impact of dispensing channel on adherence, it is important to control for bias from a patient’s predisposition to be adherent.
To our knowledge, previously published channel-adherence studies have not controlled for this potential confounder.13-15 A part of this effect, prior adherence behavior (PAB), can be controlled for by using a proxy measure—prior adherence, calculated based on pharmacy claims data. Also, most channel-adherence studies either have not fully controlled for differences in the days of supply between the 2 channels or have not taken patients’ choice of channel into account. This study aims to address the aforementioned biases and limitations, and tease out the effect of dispensing channel on adherence to medications to treat diabetes, hypertension, and high blood cholesterol.
This study used prescription claims data from a nationally representative sample of commercially insured members whose pharmacy benefits were managed by a large pharmacy benefit management company. Inclusion was limited to patients who were continuously enrolled for pharmacy benefits from April 1, 2009, until December 31, 2011, who were between the ages of 18 and 64 years, and who had any prescription claim for antidiabetics, antihypertensives, or antihyperlipidemics during the index period, which was from October 1, 2009, to December 31, 2009. Patients whose pharmacy benefit design required the use of mail order exclusively for maintenance medications or did not allow access to mail order (mandatory retail) at any time during the entire study period were excluded from analysis. That is, only those patients who were free to choose either channel at any time during the study to fill their maintenance prescriptions were selected. Under provisions of the Health Insurance Portability and Accountability Act of 1996, all data specific to individual patients were removed to maintain the privacy of protected health information from internal analytical data sets. All prescription claims were adjusted to 30-day equivalents.
A retrospective claims analysis over a 3-year period divided into 4 distinct phases (Figure) was conducted. A 6-month look-back period from April to September 2009 was used to assess whether the patients were new or continuing users of the medications identified. Patients having a claim within the same therapy class under study in the look-back period were categorized as continuing users and those without claims as new users. This indicator attempted to capture any differences in adherence that resulted from the longevity of treatment. The analysis period for this study was from January 1, 2011, to December 31, 2011. As previous adherence may be indicative of a health-conscious personality and a measure of better health-seeking behavior,22 a patient’s prior adherence was used as a proxy control for self-selection bias due to the PAB effect in the multivariate model. Prior adherence was based on the patient’s medication possession ratio (MPR) in the year 2010, termed as the baseline period.
The primary outcome measure was patient adherence to diabetes, hypertension, or high blood cholesterol medications, defined as an MPR of 80% or greater23 in the analysis period. Patients’ MPR was calculated as the total days of supply divided by 365 days, capping it at 100%. At the drug group level, the combination of 8-digit Generic Product Identifier (GPI) codes and clinically appropriate drug groups was used to calculate the MPR, which then was averaged to the therapy class level for each patient (eAppendix A, available at www.ajmc.com). Drug groups were based on clinically accepted drug subclasses within each therapy class. Only the numbers of medication units actually meant to be taken during the study periods were included in calculations. That is, the parts of any claim that were in possession before the key periods (2010 for baseline and 2011 for analysis) and any excess in possession after the ends of the periods were excluded from the adherence calculations.
Based on a literature review, independent variables to be included in the model were identified. In addition to dispensing channel, other independent variables included prior adherence, age, sex, OOP costs for 30-day adjusted prescriptions, disease burden, severity of illness, location (urbanicity) of the patient, and average days of supply per claim. Channel was assigned to individuals based on where they obtained at least two-thirds (66.7%) of their 30-day adjusted prescriptions. Those who did not receive at least 66.7% of their 30-day adjusted prescriptions from either mail order or retail were assigned to a mixed channel group. Prior adherence was included in the model to control for the PAB effect, as past health behavior has been known to be a good marker for predicting future health behavior.24 A similar method was used in a 2011 study examining the association between statin use and outcomes that used prior adherence to control for the healthy-adherer effect.22 The MPR for 2010 was calculated for each patient to establish prior adherence, and patients with an MPR of 80% or greater were classified as adherent.13,23,25
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