The study evaluated the efficacy and safety of bosentan, an 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 bosentan at two doses (62.5 mg or 125/250 mg twice daily) for a minimum of 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 a significant improvement in walking distance (mean difference of 44 m, P=0.001), Borg dyspnea index, WHO functional class, and time to clinical worsening. The 125 mg dose was well tolerated, while the 250 mg dose led to a higher frequency of abnormal liver function tests. The study concluded that bosentan is beneficial and well-tolerated in patients with PAH, particularly at a dose of 125 mg twice daily.The study evaluated the efficacy and safety of bosentan, an 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 bosentan at two doses (62.5 mg or 125/250 mg twice daily) for a minimum of 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 a significant improvement in walking distance (mean difference of 44 m, P=0.001), Borg dyspnea index, WHO functional class, and time to clinical worsening. The 125 mg dose was well tolerated, while the 250 mg dose led to a higher frequency of abnormal liver function tests. The study concluded that bosentan is beneficial and well-tolerated in patients with PAH, particularly at a dose of 125 mg twice daily.