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Evaluation of daptomycin activity against Staphylococcus aureus in an in vitro pharmacodynamic model under normal and
Vanthida Huang1, Michael J Rybak
1Anti-Infective Research Laboratory, Department of Pharmacy Practice, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, MI 48201, USA.
Objectives:
Daptomycin is a lipopeptide antimicrobial that is primarily excreted by the kidney. We examined daptomycin bactericidal activity in an in vitro pharmacodynamic model (IVPM) under normal and simulated impaired renal function against methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA).
Methods:
Two clinical strains MSSA-1199 and MRSA-494 were used in an IVPM. MICs and MBCs were determined according to CLSI. Daptomycin free concentrations were simulated that corresponded to dose regimens of 4, 6 and 8 mg/kg every 24 h at 8 h t(1/2) (Scheme I) and every 48 h at 30 h t(1/2) (Scheme II). In addition, we simulated daptomycin free concentrations corresponding to fractional dose regimens of 2, 3 and 4 mg/kg every 24 h at 30 h t(1/2) (Scheme III). The targeted C(max free)/MIC for 2, 3, 4, 6 and 8 mg/kg against MSSA-1199 ranged from 5.2 to 21.2. The targeted C(max free)/MIC for 2, 3, 4, 6 and 8 mg/kg against MRSA-494 ranged from 10.4 to 42.2. The targeted AUC(free)/MIC for Schemes I, II and III against MSSA-1199 ranged from 94 to 392. The targeted AUC(free)/MIC for Schemes I, II and III against MRSA-494 ranged from 188 to 581. Bactericidal activity and the potential for resistance were determined over 96 h. All models were completed in triplicate.
Results:
Daptomycin MICs (MBCs) for MSSA-1199 and MRSA-494 were 0.5 (1.0) mg/L and 0.25 (0.25) mg/L, respectively. Daptomycin 6 and 8 mg/kg at both 8 and 30 h t(1/2) achieved 99.9% kill as early as 1 h. Daptomycin 4 mg/kg achieved 99.9% kill as early as 1 h when given at 8 and 30 h t(1/2) but was not maintained to an endpoint of 96 h (P > 0.05).
Conclusions:
Overall, there was no difference in kill noted for daptomycin regimens at 4, 6 and 8 mg/kg every 24 h at 8 h t(1/2) versus every 48 h at 30 h t(1/2). Fractional doses of daptomycin at 30 h t(1/2) were inferior to daptomycin regimens of 4, 6 and 8 mg/kg administered every 48 h (P = 0.03).
Insights
Daptomycin effectively kills Staphylococcus aureus, including MRSA, with standard dosing regimens. Fractional doses showed reduced efficacy, highlighting the importance of appropriate dosing in renal impairment.
Area of Science:
- Pharmacology
- Infectious Diseases
- Nephrology
Background:
- Daptomycin is a lipopeptide antimicrobial primarily cleared by the kidneys.
- Renal impairment may affect daptomycin efficacy due to altered drug pharmacokinetics.
Purpose of the Study:
- To evaluate daptomycin's bactericidal activity against Staphylococcus aureus (MSSA and MRSA) in an in vitro pharmacodynamic model simulating normal and impaired renal function.
- To compare different daptomycin dosing regimens and their impact on antimicrobial efficacy.
Main Methods:
- An in vitro pharmacodynamic model (IVPM) was used with methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) strains.
- Simulated daptomycin concentrations reflected various dosing regimens (4, 6, 8 mg/kg every 24h or 48h) and half-lives (8h and 30h) to mimic normal and impaired renal function.
- Bactericidal activity and resistance development were assessed over 96 hours.
Main Results:
- Daptomycin demonstrated potent bactericidal activity, achieving 99.9% kill of MSSA and MRSA rapidly at 6 and 8 mg/kg doses.
- A 4 mg/kg dose achieved rapid kill but efficacy was not sustained over 96 hours.
- No significant difference in kill was observed between standard 24-hour and extended 48-hour dosing intervals at 8 mg/kg.
Conclusions:
- Standard daptomycin dosing regimens (4, 6, 8 mg/kg) every 24 or 48 hours show comparable efficacy in vitro.
- Fractional daptomycin dosing regimens were found to be inferior, suggesting that maintaining adequate drug exposure is crucial.
- These findings support the use of standard dosing in patients with renal impairment, while cautioning against fractional dosing.
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