Comparing the Sensitivities of Measures of Adherence to Antihypertensive Drugs Using Korean National Health Insurance Claims Data

Abstract

Purpose Numerous studies have utilized various forms of adherence measures. However, methods for measuring adherence are inconsistent. Moreover, few studies are available that have compared sensitivities of the effects of several criteria on medication adherence. This study aims to compare measures of adherence using varied analytical decisions. Materials and Methods We included three measures for adherence: proportion of days covered with one or more medications (PDC with≥1 ), duration weighted mean PDC (PDC wm ), and daily polypharmacy possession ratio (DPPR). We compared the sensitivities of the measures by changing parameters in the Korean nationwide claims database. First, we used PDC with≥1 as our base model. Then, we divided an adherence measure algorithm into three categories: (1) definition of data cleaning, (2) inclusion criteria and observation period, and (3) calculation methods of medication adherence. The categories included eight decision nodes that incorporated 25 alternative options. Finally, we assessed the medication adherence for the base-case with commonly used values and then varied to measure with each alternative option. Results The base-case included 14,288 beneficiaries with antihypertensives. Among eight decisions, both handling an end-date-of-study and overlaps had the strongest impacts on measuring PDC with≥1 , PDC wm , and DPPR, with small differences in sample size. Instead of the estimates of adherence from PDC wm , those of PDC with≥1 and DPPR were similar. Furthermore, a tendency toward a higher medication adherence was observed with a smaller study population. Conclusion The decisions regarding identifying an end-date-of-study and overlaps showed meaningful impacts of all three measures including PDC with≥1 , PDCwm, and DPPR on measuring medication adherence.

A comparison of methods for the measurement of adherence to antihypertensive multidrug therapy and the clinical consequences: a retrospective cohort study using the Korean nationwide claims database

“…As there were no previous studies comparing these 3 measurements in multidrug antihypertensive therapy, it is difficult to directly compare to previous studies. Our previous study of patients receiving both antihypertensive single and multidrug regimens showed similar trends [ 22 ]. However, a previous study comparing adherence to antidiabetic therapy showed different trends; the median value (IQR) of adherence was 95.9% (IQR, 72.3-100) and 77.5% (IQR, 51.8-96.4) when using PDC with≥1 and DPPR, respectively [ 33 ].…”

“…To compare the measurements of adherence to multidrug antihypertensive therapy and their clinical consequences, we included PDC with≥1 , PDC wm , and DPPR, which had been analyzed in our previous study [ 17 - 20 , 22 ]. First, PDC with≥1 was calculated as the number of days covered by ≥ 1 prescription during the observation period, divided by the number of days from the first prescription to the end of the observation period [ 17 , 19 ].…”

“…In addition, we compared 2 approaches (PxM and FxM) to defining the end-date of the study, which had been shown to be a potentially significant factor when measuring adherence in previous studies [ 22 , 26 - 28 ]. The PxM approach assumes that a patient takes the medication from the first prescription fill to the end of the supply of the last refill, while the FxM approach assumes that a patient takes the medication during the entire observation period ( Supplementary Material 1 ).…”

“…Second, the results of studies analyzing various approaches to medication use have been inconsistent [ 17 , 21 , 22 ]. Observational studies have reported that patients took their medications as prescribed, that patients refilled prescriptions before their previous supply was depleted, or that patients took extra doses accumulated during the observation period [ 21 , 22 ]. Nevertheless, the comparative validity of these results remains unclear.…”

“…In a previous study we compared the 3 abovementioned measurements of adherence to antihypertensive medications and developed an algorithm of 8 different approaches incorporating 25 alternative assumptions [ 22 ]. We suggested that PDC with≥1 could be the preferred option.…”