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Antimicrobial Agents and Chemotherapy, October 1998, p. 2710-2717, Vol. 42, No. 10
The Anti-Infective Research Laboratory,
Received 27 February 1998/Returned for modification 25 May
1998/Accepted 20 July 1998
Quinupristin-dalfopristin is a streptogramin antibiotic combination
with activity against vancomycin-resistant Enterococcus faecium (VREF), but emergence of resistance has been recently reported. We studied the activity of quinupristin-dalfopristin against
two clinical strains of VREF (12311 and 12366) in an in vitro
pharmacodynamic model with simulated endocardial vegetations (SEVs) to
determine the potential for resistance selection and possible
strategies for prevention. Baseline MICs/minimal bactericidal concentrations (µg/ml) for quinupristin-dalfopristin, quinupristin, dalfopristin, and doxycycline were 0.25/2, 64/>512, 4/512, and 0.125/8
for VREF 12311 and 0.25/32, 128/>512, 2/128, and 0.25/16 for VREF
12366, respectively. Quinupristin-dalfopristin regimens had
significantly less activity against VREF 12366 than VREF 12311. An
8-µg/ml simulated continuous infusion was the only bactericidal regimen with time to 99.9% killing = 90 hours. The
combination of quinupristin-dalfopristin every 8 h with
doxycycline resulted in more killing compared to either drug alone.
Quinupristin-dalfopristin-resistant mutants (MICs, 4 µg/ml;
resistance proportion, ~4 × 10
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Treatment of Vancomycin-Resistant Enterococcus faecium
with RP 59500 (Quinupristin-Dalfopristin) Administered
by Intermittent or Continuous Infusion, Alone or in
Combination with Doxycycline, in an In Vitro Pharmacodynamic
Infection Model with Simulated Endocardial Vegetations
4) emerged during
the quinupristin-dalfopristin monotherapies for both VREF strains.
Resistance was unstable in VREF 12311 and stable in VREF 12366. The
8-µg/ml continuous infusion or addition of doxycycline to
quinupristin-dalfopristin prevented the emergence of resistance for
both strains over the 96-h test period. These findings replicated the
development of resistance reported in humans and emphasized bacterial
factors (drug susceptibility, high inoculum, organism growth phase) and
infectious conditions (penetration barriers) which could increase
chances for clinical resistance. The combination of
quinupristin-dalfopristin with doxycycline and the administration of
quinupristin-dalfopristin as a high-dose continuous infusion warrant
further study to determine their potential clinical utility.
*
Corresponding author. Mailing address: The
Anti-Infective Research Laboratory, Department of Pharmacy Services
(1B), Detroit Receiving Hospital and University Health Center, 4201 St.
Antoine Blvd., Detroit, MI 48201. Phone: (313) 745-4554. Fax: (313)
993-2522. E-mail: mrybak{at}dmc.org.
Antimicrobial Agents and Chemotherapy, October 1998, p. 2710-2717, Vol. 42, No. 10
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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