Avanafil is a potent and selective inhibitor of phosphodiesterase type 5 (PDE5) with IC50 value of 5.2nM [1].

PDE5 is abundantly expressed in penile corpus cavernosum and regulates penile blood flow by regulating the cGMP concentration. PDE5 inhibitors are similar in structure to cGMP and competitively bind to PDE5, resulting in the inhibition of cGMP hydrolysis. Avanafil is a high selective inhibitor of PDE5 with Ki value of 4.3nM and is developed for the treatment of erectile dysfunction. It shows high selectivity against other PDE enzymes of the PDE family. In the intravenous study, the administration of avanafil at 300μg/kg can potentiate penile tumescence. The calculated ED200% of avanafil on tumescence is 37.5μg/kg and the plasma concentration is 59.6ng/ml. Additionally, avanafil potentiates penile tumescence at a dose range of 100 to 1,000μg/kg intraduodenally. And the ED200% is 151.7μg/kg [1, 2].

References:
[1] Kotera J, Mochida H, Inoue H, Noto T, Fujishige K, Sasaki T, Kobayashi T, Kojima K, Yee S, Yamada Y, Kikkawa K, Omori K. Avanafil, a potent and highly selective phosphodiesterase-5 inhibitor for erectile dysfunction. J Urol. 2012 Aug;188(2):668-74.
[2] Cui YS, Li N, Zong HT, Yan HL, Zhang Y. Avanafil for male erectile dysfunction: a systematic review and meta-analysis. Asian J Androl. 2014 May-Jun;16(3):472-7.