CKD-828 S-Amlodipine Non-Responder Trial

Inclusion Criteria: * age 18 years or older * diagnosis of essential hypertension and blood pressure not adequately controlled (inadequate control defined as seated diastolic blood pressure(DBP)≥ 90mmHg if on existing amtihypertensive treatment of seated DBP≥100mmHg if treatment naive) * failure to respond to four weeks treatment with S-Amlodipine 2.5mg(failure to respond defined as seated DBP ≥ 90mmHg) * willing and able to provide written informed consent Exclusion Criteria: * mean seated DBP ≥ 120mmHg and/or mean seated SBP ≥ 200mmHg during run-in treatment or mean seated DBP ≥ 120mmHg and/or mean seated SBP ≥ 180mmHg at the randomization visit * known or suspected secondary hypertension(ex. aortic coarctation, Primary hyperaldosteronism, renal artery stenosis, pheochromocytoma) * has severe heart disease(Heart failure NYHA functional class 3, 4), unstable angina or myocardial infarction, arrhythmia within the past three months * has cerebrovascular disease as cerebral infarction, cerebral hemorrhage within 6 months * Type I Diabetes Mellitus, Type II Diabetes Mellitus with poor glucose control as defined by fasting glucosylated hemoglobin(HbA1c) \> 8% * known severe or malignant retinopathy * hepatic or renal dysfunction as defined by the following laboratory parameters: AST/ALT \> UNL X 2, serum creatinine \> UNL X 1.5 * acute or chronic inflammatory status need to treatment * need to additional antihypertensive drugs during the study * need to concomitant medications known to affect blood pressure during the study * history of angioedema related to ACE inhibitors or Angiotensin II Receptor Blockers * known hypersensitivity related to either study drug * history of drug or alcohol dependency within 6 months * any surgical or medical condition which might significantly alter the absorption, distribution, metabolism, or excretion of investigational products(ex. gastrointestinal tract surgery such as gastrectomy, gastroenterostomy or bypass, active inflammatory bowel syndrome within 12 months prior to screening, gastric ulcers need to treatment, gastrointestinal/rectal bleeding, impaired pancreatic function such as pancreatitis, obstructions of the urinary tract or difficulty in voiding * administration of other study drugs within 30 days prior to randomization * premenopausal women(last menstruation \< 1year) not using adequate contraception, pregnant or breast-feeding * history of malignancy including leukemia and lymphoma within the past 5 years * in investigator's judgment