The study evaluated the efficacy and safety of bosentan, a dual endothelin-receptor antagonist, in patients with pulmonary arterial hypertension (PAH). In a double-blind, placebo-controlled trial, 213 patients were randomly assigned to receive either placebo or 62.5 mg of bosentan twice daily for 4 weeks, followed by either 125 mg or 250 mg of bosentan twice daily for at least 12 weeks. The primary endpoint was the change in six-minute walking distance, with secondary endpoints including the Borg dyspnea index, World Health Organization (WHO) functional class, and time to clinical worsening. After 16 weeks, patients treated with bosentan showed an average improvement of 44 meters in six-minute walking distance compared to the placebo group (P=0.001). Bosentan also improved the Borg dyspnea index and WHO functional class and increased the time to clinical worsening. The study concluded that bosentan is beneficial for patients with PAH and is well tolerated at a dose of 125 mg twice daily.The study evaluated the efficacy and safety of bosentan, a dual endothelin-receptor antagonist, in patients with pulmonary arterial hypertension (PAH). In a double-blind, placebo-controlled trial, 213 patients were randomly assigned to receive either placebo or 62.5 mg of bosentan twice daily for 4 weeks, followed by either 125 mg or 250 mg of bosentan twice daily for at least 12 weeks. The primary endpoint was the change in six-minute walking distance, with secondary endpoints including the Borg dyspnea index, World Health Organization (WHO) functional class, and time to clinical worsening. After 16 weeks, patients treated with bosentan showed an average improvement of 44 meters in six-minute walking distance compared to the placebo group (P=0.001). Bosentan also improved the Borg dyspnea index and WHO functional class and increased the time to clinical worsening. The study concluded that bosentan is beneficial for patients with PAH and is well tolerated at a dose of 125 mg twice daily.