BACKGROUND: Omadacycline is an amino-methylcycline antibiotic that is indicated for the treatment of adults with community-acquired bacterial pneumonia (CABP) and acute bacterial skin and skin structure infections (ABSSSI). Like many new antibiotics, there are scant real-world effectiveness data for omadacycline. There is also a high potential that an omadacycline prescription is rejected or reversed, and it is not known whether patients who have an unapproved omadacycline claim are at higher risk for 30-day emergency department (ED)/inpatient (IP) visits. OBJECTIVE: To describe the real-world effectiveness of omadacycline and assess the impact of unapproved omadacycline claims among adult outpatients with CABP or ABSSSIs. METHODS: The study population included patients who received 1 or more omadacycline outpatient prescriptions from a large US claims database (October 2018 to September 2020) and had a diagnosis for CABP or ABSSSI. The approval status of omadacycline claims was determined. The proportion of all-cause 30-day ED/IP visits among patients with an approved vs unapproved claim was compared. RESULTS: 404 patients met the inclusion criteria (CABP: 97; ABSSSI: 307). Of the 404 patients, 146 (36%) had an unapproved claim (CABP: 28; ABSSSI: 118). Overall, the proportion of 30-day ED/IP visits (yes/no) for those with an unapproved and approved claim was 28% vs 17%, respectively (P < 0.05). The overall adjusted 30-day ED/IP visits incidence difference was 11% (95% CI = 2 - 19), corresponding to an adjusted number needed to treat of 9 (95% CI = 5 - 43). CONCLUSIONS: A high incidence (36%) of unapproved omadacydine claims was observed in this study. Patients with unapproved daims had an 11% higher incidence of 30-day all-cause ED/IP visits than patients with approved claims. DISCLOSURES This study was funded by Paratek Pharmaceuticals, Inc (King of Prussia, PA). Dr Lodise is a consultant to Paratek Pharmaceuticals, Inc, and has received consultancy payments. Drs Gunter, Sandor, and Berman are employees and shareholders of Paratek Pharmaceuticals, Inc. Dr Mu, Ms Gao, Ms Yang, and Ms Yim are employees of Analysis Group. Analysis Group has received payment from Paratek Pharmaceuticals, Inc, to conduct part of this study.