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Combination therapy may be effective against S. maltophilia
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Meropenem plus levofloxacin demonstrated Etest synergy in 60% of Stenotrophonomas maltophilia isolates, according to study results presented at the 2010 Annual Conference on Antimicrobial Resistance.
From May 2007 to June 2009, study researcher George A. Pankey, MD, a member of the Infectious Disease News editorial board, and colleagues, collected 20 genetically unique clinical S. maltophilia isolates from patients to evaluate potential synergistic activity of meropenem plus levofloxacin against S. maltophilia. The researchers used Etest MICs and synergy method, which was performed in triplicate with the summation fractional inhibitory concentration calculated for each set of MICs, and the mean used for comparison to the time-kill assay (TKA). Isolates had the following susceptibility:
- 35% sensitive to ceftazidime;
- 10% sensitive to chloramphenicol;
- 95% sensitive to minocycline;
- 35% sensitive to ticarcillin/clavulanate;
- 100% sensitive to trimethoprim/sulfamethoxazole.
Results revealed synergy with levofloxacin plus meropenem in 12 of 20 of S. maltophilia isolates, whereas eight of 20 showed indifference. TKA data indicated synergy in nine of 20 isolates, with the remaining 11 showing indifference. Researchers also found that two of three non-susceptible levofloxacin isolates also demonstrated synergy by both Etest and TKA.
Currently, the mechanism of in vitro synergy between levofloxacin and meropenem remains unclear, and more study is needed on the interaction.
In an interview, Pankey said that limited options for resistant isolates necessitates looking at combination therapies, and this combination may hold promise as a therapeutic option, but in vivo studies are needed. – by Melissa Foster
Pankey G. Abstract #P18. Presented at: 2010 Annual Conference on Antimicrobial Resistance. February 1-3, 2010. Bethesda, MD.