Complex sentence: Sildenafil citrate, one of the PDE5 inhibitors, is also indicated for the treatment of pulmonary hypertension, and the chemically related drugs tadalafil and vardenafil have been studied as other possible treatments for this disease.
Split into simpler sentences: Sildenafil citrate, one of the PDE5 inhibitors, is also indicated for the treatment of pulmonary hypertension. Other PDE5 inhibitors such as tadalafil and vardenafil have been studied as other possible treatments for this disease.