Relationship Between Adherence to Antihypertensive Medication Regimen and Out-of-Pocket Costs Among People Aged 35 to 64 With Employer-Sponsored Health Insurance

Madeleine M. Baker-Goering, PhD; Kakoli Roy, PhD; David H. Howard, PhD


Prev Chronic Dis. 2019;16(3):e32 

In This Article


We used 2014 administrative claims data from the IBM MarketScan Commercial Database (IBM Corp), which provided de-identified health care claims data for enrollees and their dependents in employer-sponsored health insurance plans. We limited the study sample to adults aged 35 to 64 who were continuously enrolled with prescription drug coverage in 2014 (N = 3,362,633). We focused on 2014 after using the IBM Treatment Pathways online tool (IBM Corp), which reported stable trends of proportions of patients with any hypertension diagnosis (25%−26%) and proportions of patients filling an antihypertensive medication prescription (29%−30%) in 2010 through 2014.

We identified people with hypertension by the appearance of International Classification of Diseases, 9th Revision (ICD-9), diagnosis codes (401.x–405.x) on at least 2 outpatient or 1 inpatient or emergency department claim, and we identified cardiovascular disease events resulting in an inpatient or emergency department visit by using ICD-9 codes from the Center for Medicare and Medicaid Services' Chronic Conditions Warehouse for ischemic heart disease, acute myocardial infarction, cerebrovascular disease, and heart failure (398.91, 402.x–404.x, 410.x, 411.x–413.x, 414.0x, 414.12, 414.2, 414.3, 414.8, 414.9, 428.x, 430.x, 431.x, 433.x1, 434.x, 436.x, 997.02).[7] We measured adherence to antihypertensive medications among enrollees with at least 1 antihypertensive drug claim in 2014. We identified antihypertensive medications by Redbook drug codes for therapeutic class (except for angiotensin II receptor blockers, which we identified by using National Drug Codes, because they were not identified in Redbook by therapeutic class).[8] We measured the proportion of days covered (days covered equaled the patient's supply of medication from the day of the first filled prescription through the end of the calendar year), divided by the number of days in that same period, calculated for each medication class, and then averaged across number of medication classes per person. Enrollees with less than 80% of days covered were considered nonadherent, a cutoff used in many studies.[4,9] We report total out-of-pocket cost (sum of copayments, coinsurance, or deductibles) and total payments for antihypertensive medications. We also reported number of filled prescriptions and out-of-pocket and total medication costs for a 30-day equivalent supply of antihypertensive medications (eg, 15 days of supply becomes 0.5 of a 30-day fill). Out-of-pocket costs was converted to a categorical variable ($0, <$5, $5–<$10, $10–<$15, $15–<$20, $20–<$50, and ≥$50).

We used multivariate logistic regression to estimate the association between category of out-of-pocket cost and the likelihood of being nonadherent and presented these data as odds ratios. We used Stata 12 SE (StataCorp, LLC) to analyze data.