New oral antibiotic contezolid (CZD) is effective against Gram-positive infections but unsuitable for intravenous (IV) administration due to its modest solubility. To address the medical need for an IV form of CZD, its isoxazol-3-yl phosphoramidate derivatives have been explored, and contezolid acefosamil (CZA, 8), the first representative of a novel O-acyl phosphoramidate prodrug class, has been identified. CZA exhibits high aqueous solubility (>200 mg/mL) and good hydrolytic stability at media pH suitable for IV administration. CZA rapidly converts into the active drug CZD in vivo. In a pharmacokinetic (PK) rat model, the exposure of active drug CZD after IV administration of the prodrug CZA was similar to or higher than that from the IV administration of CZD. The prodrug CZA is bioequivalent to or better than CZD in several preclinical infection models. CZA is likewise active upon its oral administration. To date, CZA has been evaluated in Phase 1 and Phase 2 clinical trials in the USA. It is advancing into further clinical studies including step-down therapy with in-hospital intravenous CZA administration followed by outpatient oral CZD treatment.