Study of Efficacy and Safety of Irbesartan/Amlodipine 4 Fixed Combination Therapy in Hypertensive Patients Uncontrolled on Irbesartan or Amlodipine Monotherapy

Primary Objective: \- To assess the proportion of patients with controlled Office Blood Pressure Measurements (OBPM), defined as Systolic blood pressure \< 140 mmHg and Diastolic blood pressure \<90mmHg, at the end of the study Secondary Objectives: * To examine over time the antihypertensive effect of the 4 doses of the fixed combination therapy irbesartan/amlodipine on OBPM (SBP (systolic blood pressure) and DBP (diastolic blood pressure) * To examine the proportion of patients with controlled OBPM (systolic BP\<140 mm Hg and diastolic BP\<90 mmHg) of the different dose groups over time * To determine the incidence and severity of adverse events.