Associations of Chronic Medication Adherence with Emergency Room Visits and Hospitalizations.

INTRODUCTION Good medication adherence is associated with decreased healthcare expenditure; however, adherence is usually assessed for single medication. We aim to explore the associations of adherence levels to 23 chronic medications with emergency room (ER) visits and hospitalizations. The primary endpoints are ER visits and hospitalizations in internal medicine and surgical wards. METHODS Individuals aged 50-74 years, with a diagnosis of diabetes mellitus or hypertension, treated with at least one antihypertensive or antidiabetic medication during 2017 were included. We determined personal adherence rates by calculating the mean adherence rates of the medications prescribed to each individual. Adherence rates were stratified into categories. We retrieved information about all the ER visits, and hospitalizations in internal medicine and surgical wards during 2016-2018. RESULTS Of 268,792 persons included in the study, 50.6% were men. The mean age was 63.7 years. Hypertension was recorded for 217,953 (81.1%), diabetes for 160,082 (59.5%), and both diabetes and hypertension for 109,225 (40.6%). The mean number of antihypertensive and antidiabetic medications used was 2.2 ± 1.1. In total, 51,301 (19.1%) of the cohort visited the ER at least once during 2017, 21,740 (8.1%) were hospitalized in internal medicine wards, and 10,167 (3.8%) in surgical wards during 2017. Comparing the highest adherence category to the lowest, adjusted odds ratios were 0.64 (0.61, 0.67) for ER visits, 0.56 (0.52, 0.60) for hospitalization in internal wards, and 0.63 (0.57, 0.70) for hospitalization in surgical wards. Odds ratios were similar for the three consecutive years 2016-2018. CONCLUSION Better medication adherence was associated with fewer ER visits and hospitalizations among persons with diabetes and hypertension. Investing in improving medication adherence may reduce health costs and improve patients' health.