• Forearm vascular resistance [ Time Frame: At baseline and end of study ] [ Designated as safety issue: No ]
• Changes of serum TBARS, CRP, IL-6, and VCAM-1 [ Time Frame: Throughout the study period ] [ Designated as safety issue: No ]
• Office BP measurement of seated SBP and DBP [ Time Frame: At baseline and after 12-week treatment ] [ Designated as safety issue: No ]
• Adverse events [ Time Frame: Throughout the study period ] [ Designated as safety issue: Yes ]

• Forearm vascular resistance
• Changes of serum TBARS, CRP, IL-6, and VCAM-1
• Office BP measurement of seated SBP and DBP at baseline and after 12-week treatment
• Adverse events

• Safety
• The incidence of adverse events and marked laboratory abnormalities in each treatment will be compared using Chi square or Fisher's Exact Test

Primary:

1. To compare the change in forearm vascular resistance following a 12-week regimen of irbesartan/hydrochlorothiazide versus irbesartan
2. To assess changes of serum proinflammatory cytokine, markers of cardiovascular risks, oxidative stress and circulating adhesion molecule including thiobarbiturate acid reactive substances (TBARS), C-reactive protein (CRP), interleukin 6 (IL-6), and vascular cell adhesion molecule 1 (VCAM-1).

Secondary:

1. To compare the reduction in office blood pressure following a 12-week regimen of irbesartan/hydrochlorothiazide versus irbesartan
2. To compare the response rate (defined as office Systolic blood pressure(SBP)/diastolic blood pressure (DBP) reduce more than 10mmHg from baseline), and BP controlled rate (defined as SBP<140 mmHg and /or DBP<90 mmHg)
3. To ascertain the safety and tolerability of irbesartan / hydrochlorothiazide versus irbesartan when administered once daily
4. To determine whether angiotensin II type 1 (AT-1) receptor gene polymorphisms (including A1166C gene with about 4% of the minor allele frequency in Chinese population and other single nucleotide polymorphisms with a higher frequency of about 10% of minor allele) is related to reduction of BP

• Drug: Irbesartan/Hydrochlorothiazide
• Drug: Irbesartan

• Experimental:
  • 12 weeks on treatment 1
  • 2 week washout period
  • 12 weeks on treatment 2
• Experimental:
  • 12 weeks on treatment 2
  • 2 week washout period
  • 12 weeks on treatment 1

Inclusion Criteria:

Patients with mild to moderate hypertension with office diastolic BP (DBP) 90-109 mmHg and/or systolic BP (SBP) 140-179 mmHg before entering each treatment

Exclusion Criteria:

• females: who are pregnant or breast feeding
• office DBP ≧ 110 mmHg or office SBP ≧ 180 mmHg
• history of significant cardiovascular diseases which include: acute myocardial infarction within six months or any ischemic heart disease requiring medication, or cerebrovascular disease
• history of significant renal diseases including: serum creatinine > 3.0 mg/dl, or creatinine clearance < 30 ml/min.
• severe biliary cirrhosis and cholestasis
• refractory hypokalemia, hypercalcemia
• history of autoimmune disease, collagen vascular disease, multiple drug allergies, bronchospastic disease or other malignancies requiring current medication
• hepatic disease as indicated by any of the following : Serum Glutamic Oxaloacetic Transaminase (SGOT) or Serum Glutamic Pyruvate Transaminase (SGPT) >3 x upper limit of normal, or serum bilirubin > 2 x upper limit of normal

The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial.