Methods: Study SD001 was a Phase 2 multicenter, randomized, double-blind efficacy and safety study of ORI in adults with ABSSSI. Patients received IV ORI either as a 1200 mg dose, 200 mg once daily for 3-7 days, or 800 mg on Day 1 plus 400 mg on Day 5, at the Investigator’s discretion. Nasal swabs were collected from patients at baseline and at the Test-of-Cure (ToC) visit (Day 21-29). S. aureus isolates cultured from swabs locally were sent to a central laboratory for susceptibility testing against ORI, VAN and other comparators by broth microdilution (CLSI M7 guidelines).
Results: Overall, 124 patients had nasal swabs performed at baseline and ToC. A total of 29 pairs (baseline and ToC) of S. aureus isolates, 44.8% of which were MRSA, were available for confirmatory susceptibility testing. The median interval between baseline and ToC visit in these 29 patients was 22 days. ORI MIC range (0.015-0.12 µg/mL; 100% susceptible) and MIC50/MIC90 (0.03/0.06 µg/mL) were identical for baseline and ToC isolates. VAN MIC range (0.25-1/2 µg/mL; 100% susceptible) and MIC50/MIC90 (0.5/1 µg/mL) were within 2-fold for baseline and ToC isolates. ORI and VAN MICs of all ToC isolates were within 2-fold of respective MICs of the corresponding isolate at baseline.
Conclusion: In this Phase 2 study, one quarter of tested patients carried S. aureus in the anterior nares both at baseline and at ToC. ORI and VAN MICs of S. aureus isolates from ToC were within 2-fold of the MICs of the corresponding baseline isolates, suggesting that IV ORI treatment was not associated with changes in susceptibility to either ORI or VAN among nasal carriage isolates of S. aureus in patients with ABSSSI in this study.
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