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Synergy between orally bioavailable antibiotics and dalbavancin against MRSA

Ahrendt E, Foreman MCL, Werth BJ

The Journal of antimicrobial chemotherapy, 2026

Abstract

Background: We have shown that dalbavancin exposure can select for mutants with reduced susceptibilities to vancomycin and daptomycin, and several clinical cases of such resistance have been documented. Synergistic antimicrobial combinations may reduce resistance selection and enhance the activity of dalbavancin for deep-seated infections. Since the key advantage of dalbavancin is its infrequent dosing, the objective of this study was to evaluate whether orally bioavailable antibiotics typically dosed ≤ twice daily were synergistic with dalbavancin.

Methods: Using five isogenic S. aureus strain pairs (susceptible parent strain and a dalbavancin-selected resistant strain), we assessed for synergy between dalbavancin and cefadroxil, trimethoprim, doxycycline, moxifloxacin, and clarithromycin by standard time-kill methods.

Results: Cefadroxil was synergistic with dalbavancin against every strain tested. When combined with dalbavancin, trimethoprim was synergistic against 6/8 trimethoprim-susceptible strains, moxifloxacin was synergistic against 6/10 strains, doxycycline was synergistic against 2 strains but antagonistic against 2 strains, and clarithromycin was synergistic against 2/6 clarithromycin-susceptible strains. All other interactions were indifferent.

Conclusions: Cefadroxil is a first-generation cephalosporin, like cephalexin, but with a longer half-life that allows for a typical 12-h dosing interval. In our study, we found that synergy between cefadroxil and…

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