The purpose of the study is to evaluate the efficacy and safety of the study drug relative to an active comparator losartan which the same class of drug and is approved for use in the pediatric population aged 6 years and older. Approximately 260 subjects will participate in a 6-week, double-blind, randomized, treatment phase, followed by a 2-week, double-blind, randomized placebo-controlled withdrawal phase. This study also includes a 44-week, open-label extension (OL Phase) in which all subjects will receive AZM and other antihypertensive medications (if needed) in order to reach an optimal blood pressure. Blood pressure will be assessed in the clinic throughout the study, and subjects may also participate in a 24-hour ambulatory blood pressure monitoring (ABPM) procedure at baseline, at the end of the DB Phase and at the end of the OL Phase.