Ro18-5362 is the less active prodrug of Ro 18-5364. Even at concentrations as high as 0.1 mM Ro 18-5362 fails to affect significantly (H⁺+K⁺)-ATPase activity and associated proton translocation. In Vitro: Marked differences are seen between Ro 18-5364 (sulfoxide) and Ro18-5362 (sulfide) with regard to inhibitory activity. Even at concentrations as high as 0.1 mM Ro18-5362 fails to affect significantly (H⁺+K⁺)-ATPase activity and associated proton translocation^[1]. The sulfoxide Ro 18-5364, a potential metabolite of the IND Ro18-5362, is a powerful inhibitor of gastric mucosal (H⁺+K⁺)-ATPase, decreasing enzymatic activity with an apparent K_i of 0.1 μM^[2].