The purpose of this study is to compare the effect and safety of the antihypertensive combination therapies between losartan/amlodipine and fixed dose drug of losartan/hydrochlorothiazide.

The combination therapy with multiple antihypertensive drugs is recommended in the patients who are uncontrolled with monotherapy. Diuretics increase the activities of renin-angiotensin-aldosterone system (RAS), and angiotensin receptor blockers (ARB) depress blood pressure potently in the state of increased RAS activities. Thus, the combination therapy with ARB and diuretics is expected to lower the blood pressure synergistically. This combination therapy is also expected to reduce the side effects of each drug. In this study, we will compare the effect and safety of the combination therapies between losartan/amlodipine and fixed dose drug of losartan/hydrochlorothiazide.

Inclusion Criteria:

• Under treatment of hypertension with ARB monotherapy for more than one month.
• systolic blood pressure more than 140mmHg and less than 160mmHg or diastolic blood pressure more than 90mmHg and less than 100mmHg in sitting position.
• In diabetic or CKD patients, systolic blood pressure more than 130mmHg and less than 160mmHg or diastolic blood pressure more than 80mmHg and less than 100mmHg in sitting position.

Exclusion Criteria:

• uncontrolled hypertension (diastolic blood pressure >120mmHg)
• uncontrolled diabetes mellitus (HbA1c>9.0%)
• Acute myocardial infarction, stroke and other cardiovascular events within six months
• The history of gout, or uric acid>8.0mg/dl
• Serum creatinine>2.0mg/dl
• sever liver dysfunction
• Bilateral renovascular stenosis
• secondary hypertension
• malignant hypertension
• uncontrolled arrhythmia
• pregnancy or possibility of pregnancy
• hypersensitivity to trial drug