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Antimicrobial Agents and Chemotherapy, 07 1995, 1505-1511, Vol 39, No. 7
SL Kang and MJ Rybak
The bactericidal activity and emergence of resistance to RP 59500
(quinupristin/dalfopristin) when it was administered alone and in
combination with vancomycin against fibrin clots that have been infected
with methicillin-susceptible Staphylococcus aureus ATCC 25923 or
methicillin-resistant S. aureus (MRSA) 67 were evaluated in an in vitro
pharmacodynamic infected fibrin clot model. Fibrin clots were infected with
S. aureus to achieve an inoculum of approximately 10(9) CFU/g. Antibiotics
were administered to simulate pharmacokinetics in humans: RP 59500 (7.5
mg/kg of body weight) every 8 h and vancomycin (15 mg/kg) every 12 h over
72 h. Preliminary test tube time-kill experiments with an inoculum of
approximately 10(5) CFU/ml suggested that RP 59500 was more rapid in
achieving a 99.9% reduction in the number of CFU per milliliter than
vancomycin against ATCC 25923 (6.94 versus 24 h; P = 0.0003) and MRSA 67
(6.77 versus 17.03 h; P = 0.004). At a higher inoculum (approximately 10(8)
CFU/ml), 99.9% kill was achieved only with the combination regimen against
ATCC 25923 and MRSA 67 (10.9 and 10.5 h, respectively), with total
reductions of 6.35 and 6.33 log10 CFU/ml over 24 h, respectively. In the
fibrin clot model, RP 59500 was more effective than vancomycin in reducing
organism titers over 72 h.(ABSTRACT TRUNCATED AT 250 WORDS)
Copyright © 1995 by the American Society for Microbiology. All rights reserved.
Pharmacodynamics of RP 59500 alone and in combination with vancomycin against Staphylococcus aureus in an in vitro-infected fibrin clot model
Department of Pharmacy Services, Detroit Receiving Hospital, University Health Center, Michigan, USA.
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