The purpose of this study is to evaluate the efficacy and safety of azilsartan medoxomil, once daily (QD), co-administered with amlodipine in treating individuals with essential hypertension, compared to treatment with amlodipine alone.

Hypertension affects approximately 50 million individuals in the United States. As the population ages, the prevalence of hypertension will continue to increase if broad and effective preventive measures are not implemented. According to the World Health Organization, hypertension is the most common attributable cause of preventable death in developed nations, as uncontrolled hypertension greatly increases the risk of cardiovascular disease, cerebrovascular disease, and renal failure. Despite the availability of antihypertensive treatments, hypertension remains inadequately controlled; only about one third of patients continue to maintain control successfully.

A major component of blood pressure regulation is the renin-angiotensin-aldosterone system, a system of hormone-mediated feedback interactions that results in the relaxation or constriction of blood vessels in response to various stimuli. Angiotensin II, a polypeptide hormone, is formed from angiotensin I in a reaction catalyzed by angiotensin-converting enzyme as part of the renin-angiotensin-aldosterone system. Angiotensin II is the principal pressor agent of the renin-angiotensin-aldosterone system with a myriad of effects on the cardiovascular system and on electrolyte homeostasis.

Takeda Global Research & Development Center, Inc. is developing TAK-491 (azilsartan medoxomil) to treat patients with essential hypertension. Azilsartan medoxomil is a prodrug that is hydrolyzed to the active moiety, azilsartan, which is a selective antagonist of the angiotensin II type 1 receptor subtype.

Amlodipine is a slow-channel blocker that inhibits the transmembrane influx of calcium ions into vascular smooth muscle and cardiac muscle. It is a peripheral arterial vasodilator that acts directly on vascular smooth muscle to cause a reduction in peripheral vascular resistance and reduction in blood pressure.

This study is being conducted to determine whether administration of azilsartan medoxomil in combination with amlodipine in participants with uncontrolled hypertension is more efficacious in reducing systolic blood pressure than amlodipine alone. Participation in this study is anticipated to be approximately 10 weeks.

Inclusion Criteria:

1. Has essential hypertension and 24-hour mean systolic blood pressure greater than or equal to 140 mm Hg and less than or equal to 180 mm Hg.
2. Females of childbearing potential who are sexually active must agree to use adequate contraception, and can neither be pregnant nor lactating from Screening throughout the duration of the study
3. Has clinical laboratory evaluations within the reference range for the testing laboratory or the results are deemed not clinically significant for inclusion into this study by the investigator.
4. Is willing to discontinue current antihypertensive medications.

Exclusion Criteria:

1. Has sitting trough clinic diastolic blood pressure greater than 119 mm Hg.
2. Has a baseline 24 hour ambulatory blood pressure monitoring reading of insufficient quality.
3. The subject is hypersensitive to angiotensin II receptor blockers or calcium channel blockers.
4. Has a recent history of myocardial infarction, heart failure, unstable angina, coronary artery bypass graft, percutaneous coronary intervention, hypertensive encephalopathy, cerebrovascular accident, or transient ischemic attack.
5. Has clinically significant cardiac conduction defects.
6. Has hemodynamically significant left ventricular outflow obstruction due to aortic valvular disease.
7. Has secondary hypertension of any etiology
8. Is non-compliant with study medication during placebo run-in period.
9. Has severe renal dysfunction or disease.
10. Has known or suspected unilateral or bilateral renal artery stenosis.
11. Has a history of drug abuse or a history of alcohol abuse within the past 2 years.
12. Has a previous history of cancer that has not been in remission for at least 5 years prior to the first dose of study drug.
13. Has type 1 or poorly controlled type 2 diabetes mellitus.
14. Has hyperkalemia as defined by the central laboratory normal reference range,
15. Has an alanine aminotransferase level of greater than 2.5 times the upper limit of normal, active liver disease or jaundice.
16. Has an upper arm circumference less than 24 cm or greater than 42 cm.
17. Works night (3rd) shift.
18. Currently participating in another investigational study or has participated in an investigational study within 30 days prior to randomization.
19. Has any other serious disease or condition that would compromise subject safety or make it difficult to successfully manage and follow the subject according to the protocol.
20. Has been randomized in a previous TAK-491 study.
21. Is required to take or continues taking any disallowed medication, prescription medication, herbal treatment or over-the counter medication that may interfere with evaluation of the study medication.