Primary Nonadherence to Medications in an Integrated Healthcare Setting

Healthcare professionals and payers are constantly looking for ways to improve patient health outcomes while decreasing costs. One possible approach to this challenge is to improve medication adherence, which refers to the extent to which patients take their medications as prescribed by their provider.¹ Prior research has suggested that improved adherence is associated with better health outcomes and lower overall health costs for certain chronic diseases such as diabetes, hypertension, hypercholesterolemia, and congestive heart failure.^2-4

Most adherence research has focused on “secondary nonadherence,” which occurs when patients do not refill their prescriptions on time or they discontinue their medications altogether. A less-studied form of medication nonadherence is called “primary nonadherence” (PNA), which occurs when patients fail to pick up a newly prescribed prescription from the pharmacy.⁵ Incidence, causes, and outcomes of PNA are relatively unknown compared with those of secondary nonadherence. Since most chronic and acute diseases in the United States are often managed by prescription medications, PNA could potentially be a significant factor in determining healthcare outcomes and costs, especially if the rate of PNA is high.

PNA rates vary widely in the literature, ranging from 0.5% to 57.1% depending on the study setting, therapeutic drug group, and methodological factors such as the way PNA is defined.⁶ PNA studies in integrated healthcare delivery systems have usually been limited to medications used to treat chronic diseases such as diabetes, hyperlipidemia, and hypertension, with PNA rates ranging from 3.2% to 13% depending on the drug therapeutic group.^7,8 Examining PNA to both chronic and acute medications provides a more comprehensive understanding. Identifying risk factors associated with PNA may help clinicians target patients who are at risk.

In this study, we examined the rates and risk factors of PNA in an integrated healthcare setting across 10 drug groups which included both chronic and acute medications. Study objectives were 1) to measure PNA rates for 10 therapeutic drug groups, and 2) to identify patient, prescriber, and prescription risk factors for PNA to chronic and acute medications.

METHODS

Setting

This retrospective cohort study was conducted at Kaiser Permanente Southern California (KPSC) in Downey, California, and was approved by the KPSC Institutional Review Board. KPSC is a large managed care organization providing comprehensive healthcare to an estimated 3.3 million members at 14 medical centers. Patient information on demographics and healthcare encounters (diagnoses, procedures, laboratory results, and prescriptions) are captured in the Kaiser electronic medical record (eMR) system. KPSC members receive the majority of their healthcare and prescriptions at Kaiser Permanente facilities. Medical centers vary in population size from Kern County—serving only 92,745 patients, to San Diego—serving 490,154 members. All prescribers enter all prescriptions in the eMR system and the information is electronically sent to the Kaiser pharmacy of the patient’s choice. Copay information is only available for sold prescriptions.

Inclusion and Exclusion Criteria

A total of 10 therapeutic drug groups were selected based on disease prevalence, clinical interest, or the potential impact of PNA on healthcare outcomes: anti-infectives, analgesics, migraine medications, antidiabetics, osteoporosis medications, cardiovascular agents, antihyperlipidemics, antiasthmatics, antidepressants, and anticoagulants. The first 3 drug groups were categorized as acute therapy and the remaining were categorized as chronic therapy. Each therapeutic drug group consists of several drug classes (eAppendix A, available at www.ajmc.com). For example, the antidiabetics therapeutic drug group includes drug classes such as insulin and sulfonylureas. A total of 874 individual drug products were included in the study.

New prescriptions for a study drug prescribed between December 1, 2009, and February 28, 2010, were included. A new prescription was defined as a drug with no prior dispensing in the same drug class during the 12 months before the date the prescription was ordered (index date). For example, a sulfonylurea prescription would not be considered new if a prescription for a drug in the sulfonylurea class was dispensed during the 12 months prior to the index date. This minimized the effect of preexisting drug supplies on current filling and also excluded prescriptions used as augmentation therapy or those episodes where drugs were switched within a drug class.

Patients were required to have continuous membership and drug benefits for 12 months before and after the index date. The post-index drug benefit criterion was designed to maximize the likelihood that patients filled their medications at Kaiser rather than at outside pharmacies. The 12-month pre-index period was used to identify baseline patient characteristics. Prescriptions that were renewed, transferred from an outside pharmacy, verbally ordered by the prescriber, printed out in the doctor’s office, or were hard copy prescriptions from outside providers were excluded from the study.

Prescriptions that were switched to a different drug or later cancelled by the prescriber before being picked up by the patient were also excluded. In addition, prescriptions that had missing patient demographic information or that were filled at a Kaiser pharmacy located outside of Southern California were excluded. Lastly, since pregnancy complicates medication therapy and may result in drug discontinuation, prescriptions written for female patients who had become pregnant (based on gestation date) during the study period were excluded.

Study Outcome

The primary study outcome was PNA, which was defined as the failure to fill a prescription within 14 days of the index date. Previous studies have demonstrated that most patients fill their medications within the first 2 weeks of the index date.^7,9 Sensitivity analysis was performed to examine changes in PNA rates when the definition of PNA varied from 14 to 30 and 90 days.

Patient, Prescriber, and Prescription Characteristics