Risk Factors and the Usual Source of Care on Non-Adherence to Antihypertensive Drugs in Immigrants with Hypertension

Background: Immigrants are vulnerable to suboptimal health care utilization including non-adherence of medication use. Thus, we aimed to identify the potential risk factors of non-adherence and evaluate whether utilizing a usual source of care was associated with medication adherence in immigrants. Methods: We utilized the Korea National Health Insurance Claims Database between 2012 and 2015. Cases were immigrants who had antihypertensive prescriptions at the time of hypertension diagnosis in 2012. Controls were native-born Koreans with hypertension who were 1:1 matched to immigrants by age, sex, and Charlson comorbidity index. We used the medication possession ratio for three years to assess the adherence to antihypertensive drugs. The likelihood of non-adherence was evaluated between cases and controls by multivariate linear regression models stratified by age, sex, and number of clinic visits. We assessed the potential risk factors of non-adherence in immigrants by multivariate linear regression and logistic regression models, respectively. Results: In total, 4114 immigrants and 4114 matched native-born Koreans with hypertension were included. The mean MPR was significantly lower in immigrants (56% vs 70%, p<0.0001). Immigrants showed almost two times the level of non-adherence as native-born Koreans (odds ratio [OR], 2.01; 95% confidence interval [CI], 1.83-2.21). Stratified analyses on non-adherence presented the highest non-adherence (2.28 times) in immigrants in the younger group (30-49 years old) and the lowest non-adherence in immigrants in 65 and old group where the risk was 1.69 times higher than native Korean with the same age. The absence of a usual source of care significantly increased medication non-adherence by 1.31 to 1.58 times among immigrants. Conclusion: When the number of visited clinics increased, the degree of non-adherence increased consistently. Therefore, the systematization of registering with primary care (a usual source of care) might be a modifiable health care strategy to improve health care outcomes in immigrants.