Antihypertensive drug medication adherence and its affecting factors in South Korea.

CONTEXT Uncontrolled hypertension attributable to low medication adherence may cause such serious complications as cardiovascular disease and stroke. OBJECTIVES To estimate adherence to antihypertensive drug medication of the nation's representative sample in South Korea and to identify factors affecting medication adherence. DATA SOURCES We obtained claims data and qualification data of compulsory from the National Health Insurance, which covers almost all Korean, and identified those who got a prescription of antihypertensives during calendar year 2004. PATIENTS A total of 2,455,193 patients were included as study subjects. Cumulative medication adherence (CMA) was used as an index of medication adherence. Above 80% of CMA was defined as appropriate medication adherence. RESULTS Average CMA in the total of 2,455,193 patients was 81.4%. Appropriate adherence (CMA >or=80%) rate was 54.7% and those whose CMA is below 50% occupied 17.9%. In multiple logistic regression analysis, probability of appropriate medication adherence decreased in female gender, as age decreased, when patients have disability, when patients' residential area were from metropolitan city to city (OR: 0.91-0.92), to rural area (OR: 0.76-0.78), to extreme rural area (OR: 0.72-0.74), prescription days per visit decreased, and the number of prescribing physicians increased. CONCLUSIONS Identifying these factors in a target population or community, followed by developing intervention programs to increase antihypertensive medication adherence is needed. Also, medication adherence rate produced in this study can be used as a national health index and performance indexes of various hypertension control programs.