Impact of number of medications and age on adherence to antihypertensive medications A nationwide population-based study

This study tried to investigate the effects of number of medications and age on antihypertensive medication adherence in a real-world setting using a nationwide representative cohort. We obtained data from the National Health Insurance Service-National Sample Cohort (NHIS-NSC) of Korea, which is a sample of 2.2% (N= 1,048,061) of total population (N= 46,605,433). Patients aged 20 years or older (N = 150,550) who took antihypertensive medications for at least 1 year were selected. Medication possession ratio (MPR) was used for measuring adherence. The subjects were divided into 5 subgroups according to total number of medications: 1-2, 3-4, 5-6, 7-8, and 9 or more. The mean age and the mean number of medications were 60.3 +/- 12.6 years and 4.1 +/- 2.2, respectively. The mean MPR was 80.4 +/- 23.9%, and 66.9% (N= 100,645) of total subjects were adherent (MPR >= 80%). The overall tendency of antihypertensive medication adherence according to the total number of medications displayed an inverted U-shape with a peak at 3-4 drugs. Adherence consistently increased as the age increased until age 69 and started to decrease from age 70. The proportion of adherent patients (MPR >= 80%) according to the total number of medications also showed an inverted U-shape with a peak at 3-4 drugs. When the same number of drugs was taken, the proportion of adherent patients according to age featured an inverted U-shape with a peak at 60 to 69 years. Patients taking 9 or more total drugs had the overall odds ratio (95% CI) of non-adherence (MPR< 80%) with 1.17 (1.11-1.24) compared with those taking 1 to 8 total drugs and the odds ratios in the age subgroups of 40 to 49, 50 to 59, 60 to 69 years were 1.57 (1.31-1.87), 1.21 (1.08-1.36), and 1.14 (1.04-1.25), respectively (P<.05). Association between age, total number of medications, and antihypertensive adherence displayed an inverted U-shape with a peak at 3 to 4 total medications and at age 60 to 69 years. When the total number of drugs was 9 or more, adherence decreased prominently, regardless of age.