Effects of the endothelin receptor antagonist bosentan on hemodynamics and exercise capacity in Japanese patients with mildly symptomatic pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) trial has mostly enrolled patients with World Health Organization functional class (WHO FC) III or IV. However, PAH is rapidly progressive in nature even in patients with less severe forms at diagnosis. Following the recent studies in Western population, here we assessed the efficacy of bosentan in Japanese patients with WHO FCII PAH. In this open-label trial, bosentan 125 mg twice daily was administered for 12 weeks in 16 patients, and a hemodynamic evaluation was performed. Treatment was continued for a further 12 weeks, where the effect on exercise capacity was assessed in 13 patients. In 16 patients, mean pulmonary arterial pressure decreased from 40.4 ± 10.4 to 35.6 ± 12.6 mmHg (p = 0.018) and cardiac index increased from 2.54 ± 0.73 to 2.96 ± 0.82 L/min/m2 (p = 0.023). Thus, pulmonary vascular resistance decreased from 792 ± 565 to 598 ± 558 dyn·sec/cm5 (p = 0.006). In 13 patients followed up for 24 weeks, 6-min walking distance increased from baseline at Week 12 (p = 0.003) and Week 24 (p = 0.011). All patients were mildly symptomatic at baseline with dyspnea index (Borg scale) of 2.50 ± 1.58 and the specific activity scale (SAS) of 5.0 ± 1.4 METs. These values remained unchanged throughout the study. These results suggest that bosentan treatment was beneficial for Japanese patients with WHO FC II PAH and treatment should be started in the early stage of the disease.