Sildenafil enhances the effect of NO by inhibiting phosphodiesterase form 5 (PDE5), and that is answerable for degradation of cGMP while in the corpus cavernosum. Sildenafil has no immediate relaxant effect on isolated human corpus cavernosum. The concomitant administration in the protease inhibitor ritonavir considerably increases serum concentrations of sildenafil https://janestevensnutrition.com