Background:

Tadalafil, also known as IC351 or Cialis, is a potent, reversible and competitive small-molecule inhibitor of phosphodiesterase 5 (PDE5), a predomiant PDE in the pulmonary vasculature that hydrolyzes cyclic guanosine monophosphate (cGMP) and is involved in the pathobiology of pulmonary arterial hypertension (PAH). The inhibitory effect of tadalafil is PDE5 specific with the selectivity of 10000 times greater than that of PDE1, PDE4, PDE7, PDE8, PDE9 and PDE10 and of 780 times greater than that of PDE6. Although it is used for the treatment of erectile dysfunction through oral administration, tadalafil also improves the vasoconstrictive-predominate condition of PAH through elevating cGMP levels in pulmonary vessels resulted from PDE5 inhibition.

Reference

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