Bosentan in the treatment of pulmonary arterial hypertension with the focus on the mildly symptomatic patient

Pulmonary arterial hypertension (PAH) is a progressive disease with poor survival outcomes. Bosentan is an oral endothelin-1 receptor antagonist (ERA) that has been shown in a large randomized placebo-controlled trial (BREATHE-1) to be effective at improving exercise tolerance in patients with PAH in functional class III and IV. Further studies have been conducted showing: benefit in smaller subgroups of PAH, eg, congenital heart disease, efficacy in combination with other PAH therapies, eg, sildenafil, improved long-term survival compared with historical controls. More recently, controlled trials of new ERAs have included patients with milder symptoms; those in functional class II. Analysis of the functional class II data is often limited by small numbers. These trials have generally shown a similar treatment effect to bosentan, but there are no controlled trials directly comparing these new ERAs. The EARLY trial exclusively enrolled functional class II patients and assessed hemodynamics at 6 months. Though significant, the reduction in pulmonary vascular resistance is merely a surrogate marker for the intended aim of delaying disease progression. Significant adverse effects associated with bosentan include edema, anemia and transaminase elevation. These may preclude a long duration of treatment. Further studies are required to determine optimum treatment strategy in mild disease.