Irbesartan/Hydrochlorothiazide (HCTZ) Combination Therapy as First Line Treatment for Severe Hypertension

Inclusion Criteria: * Men and women ages 18 and older; * Willing to provide written informed consent; * Must have uncontrolled hypertension defined as: currently untreated with a diastolic blood pressure greater than 110 mmHg OR currently receiving antihypertensive monotherapy with a diastolic blood pressure greater than 100 mmHg. Monotherapy is defined as treatment with one antihypertensive medication for at least four weeks; fixed combination therapy does not represent monotherapy; * Must be willing to discontinue antihypertensive medication, if applicable; * Women of childbearing potential (WOCBP) must be using an adequate method of contraception to avoid pregnancy throughout the study and for up to one week after the study in such a manner that the risk of pregnancy is minimized. * WOCBP must have a negative serum or urine pregnancy test within 72 hours prior to the start of study medication. Exclusion Criteria: * Women who are pregnant or breastfeeding; * Known or suspected secondary hypertension; * Hypertension emergencies or stroke within the past 12 months; * Heart attack, angina or bypass surgery within the past 6 months; * Significant kidney disease; * Significant liver disease; * Systemic lupus erythematosus; * Gastrointestinal disease or surgery that may interfere with drug absorption; * Cancer during the past five years excluding localized squamous cell or basal cell carcinoma of the skin; * Currently pregnant or lactating; * Mental condition (psychiatric or organic cerebral disease) rendering the subject unable to understand the nature, scope, and possible consequences of the study; * Drug or alcohol abuse within the last five years; * Known allergy to irbesartan or diuretics.