A benzenesulfonamide derivative with vasodilatory activity. Udenafil selectively inhibits phosphodiesterase type 5 (PDE5), thus inhibiting the degradation of cyclic guanosine monophosphate (cGMP) found in the smooth muscle of the corpus cavernosa and corpus spongiosum of the penis; inhibition of cGMP degradation results in prolonged muscle relaxation, vasodilation, and blood engorgement of the corpus cavernosa, and, so, prolonged penile erection. This agent does not significantly inhibit the PDE11 isozyme; PDE11 inhibition may be associated with significant myalgia. Check for active clinical trialsusing this agent.