Efficacy in adult patients with pulmonary arterial hypertension Two randomised, double-blind, multi-centre, placebo-controlled trials have been conducted in 32 (Study AC-052-351) and 213 (Study AC-052-352, BREATHE-1) adult patients with WHO functional class III–IV pulmonary arterial hypertension (primary pulmonary hypertension or pulmonary hypertension secondary mainly to scleroderma).