15-keto Prostaglandin E2 (15-keto PGE2) is a metabolite of PGE2 formed by 15-hydroxy PGDH. In vivo, 15-keto PGE2 is essentially inactive. It has an attenuated affinity for the EP4 and EP2 receptors compared to PGE2 (Ki = 2,600-15,000 nM for the inhibition of PGE2 binding compared to a Kd = 1 nM for PGE2).