Targeting Dalbavancin Inoculum Effect: Adjunctive Single Dose of Daptomycin

Area of Science:

• Microbiology
• Infectious Diseases
• Pharmacology

Background:

• Daptomycin (DAP) is an alternative for vancomycin-resistant infections, but can lead to DAP non-susceptible (DNS) strains.
• Dalbavancin (DAL), a lipoglycopeptide, shows activity against resistant Staphylococcus aureus but is less effective at high bacterial inoculums.
• This study investigates if a minimal DAP dose can enhance DAL's efficacy against high-inoculum resistant strains.

Purpose of the Study:

• To evaluate the efficacy of dalbavancin (DAL) and daptomycin (DAP) monotherapy versus their combination against high-inoculum resistant Staphylococcus aureus.
• To determine if a single dose of DAP can mitigate the inoculum effect observed with DAL.

Main Methods:

• Broth microdilution and a one-compartment PK/PD model were used.
• Three resistant strains (two DNS-VISA, one MRSA) were tested with high (10^9 CFU/mL) and low (10^7 CFU/mL) initial inoculums.
• Evaluated DAL and DAP monotherapy and combination therapy over 168 hours.

Main Results:

• Single-agent therapies were not bactericidal at high inoculums.
• DAL monotherapy showed reduced efficacy at high versus low inoculums.
• The combination of DAL with a single DAP dose demonstrated enhanced bacterial killing at high inoculums.

Conclusions:

• Dalbavancin's inoculum effect is a significant challenge in treating high bacterial loads.
• Combining dalbavancin with a single dose of daptomycin shows promise for eradicating resistant Staphylococcus aureus strains.
• This combination strategy may be a viable option for infections with substantial bacterial burden.