Guidelines recommend the use of monotherapy of CCB, all licensed ERA drugs (ambrisentan, bosentan, and macitentan), and PDE5-i drugs (sildenafil and tadalafil), iloprost, and treprostinil as class I agents according to the World Health Organization functional class (WHO-FC).[25] Approximately 20% of patients received non-target therapy (CCB), 18% received PAH-specific monotherapy, and 62% received PAH-specific combination therapy. This evidence concerns the gene PDE5A and pulmonary arterial hypertension.