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Antimicrob. Agents Chemother., 11 1997, 2497-2501, Vol 41, No. 11
HH Houlihan, RC Mercier and MJ Rybak
We compared the pharmacodynamic activities of vancomycin with or without
gentamicin in an in vitro infection model with methicilin- resistant
Staphylococcus aureus-infected fibrin-platelet clots. Infected
fibrin-platelet clots (FPCs) were prepared with human cryoprecipitate,
human platelets, thrombin, and the organism (approximately 10[9] CFU of
MRSA-494/g) and were suspended with monofilament line in an infection model
capable of simulating human pharmacokinetics. Antibiotics were bolused to
simulate vancomycin regimens of 2 g every 24 h (q24h), 1 g q12h, 500 mg
q6h, and continuous infusion (steady-state concentration of 20 microg/ml)
and gentamicin regimens of 1.5 mg/kg of body weight q12h and 5 mg/kg once
daily (q.d.). Model experiments were performed in duplicate over 72 h. FPCs
were removed from the models in quadruplicate at 0, 8, 24, 32, 48, 72 h,
weighed, homogenized, diluted, and plated to determine colony counts. The
inoculum density at 72 h was used to compare bactericidal activities
between the regimens. All regimens containing vancomycin significantly
decreased the bacterial inoculum compared to the growth control (P <
0.001). Vancomycin monotherapy regimens were similar in bacterial kill
regardless of dosing frequency. The addition of gentamicin (either q12h or
q.d.) significantly improved the bactericidal activity of the vancomycin
q6h, q12h, and q24h regimens (P < 0.001). The greatest reduction in
bacterial density at 72 h (P < 0.001) and the most rapid rate of kill
(time to 99.9% killing) were achieved with the regimen consisting of 2 g of
vancomycin q24h plus gentamicin (q.d. or q12h).
Copyright © 1997 by the American Society for Microbiology. All rights reserved.
Pharmacodynamics of vancomycin alone and in combination with gentamicin at various dosing intervals against methicillin-resistant Staphylococcus aureus-infected fibrin-platelet clots in an in vitro infection model
Department of Pharmacy Services, Detroit Receiving Hospital/University Health Center and College of Pharmacy and Allied Health Professions, Michigan 48201, USA.
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