Evaluation of the novel combination of high-dose daptomycin plus trimethoprim-sulfamethoxazole against daptomycin-nonsusceptible methicillin-resistant Staphylococcus aureus using an in vitro pharmacokinetic/pharmacodynamic model of simulated endocardial vegetations.
Daptomycin-nonsusceptible (DNS) Staphylococcus aureus is found in difficult-to-treat infections, and the optimal therapy is unknown. We investigated the activity of high-dose (HD) daptomycin plus trimethoprim-sulfamethoxazole de-escalated to HD daptomycin or trimethoprim-sulfamethoxazole against 4 clinical DNS methicillin-resistant S. aureus (MRSA) isolates in an in vitro pharmacokinetic/pharmacodynamic model of simulated endocardial vegetations (10(9) CFU/g). Simulated regimens included HD daptomycin at 10 mg/kg/day for 14 days, trimethoprim-sulfamethoxazole at 160/800 mg every 12 h for 14 days, HD daptomycin plus trimethoprim-sulfamethoxazole for 14 days, and the combination for 7 days de-escalated to HD daptomycin for 7 days and de-escalated to trimethoprim-sulfamethoxazole for 7 days. Differences in CFU/g (at 168 and 336 h) were evaluated by analysis of variance (ANOVA) with a Tukey's post hoc test. Daptomycin MICs were 4 μg/ml (SA H9749-1, vancomycin-intermediate Staphylococcus aureus; R6212, heteroresistant vancomycin-intermediate Staphylococcus aureus) and 2 μg/ml (R5599 and R5563). Trimethoprim-sulfamethoxazole MICs were ≤0.06/1.19 μg/ml. HD daptomycin plus trimethoprim-sulfamethoxazole displayed rapid bactericidal activity against SA H9749-1 (at 7 h) and R6212 (at 6 h) and bactericidal activity against R5599 (at 72 h) and R5563 (at 36 h). A ≥8 log(10) CFU/g decrease was observed with HD daptomycin plus trimethoprim-sulfamethoxazole against all strains (at 48 to 144 h), which was maintained with de-escalation to HD daptomycin or trimethoprim-sulfamethoxazole at 336 h. The combination for 14 days and the combination for 7 days de-escalated to HD daptomycin or trimethoprim-sulfamethoxazole was significantly better than daptomycin monotherapy (P < 0.05) and trimethoprim-sulfamethoxazole monotherapy (P < 0.05) at 168 and 336 h. Combination therapy followed by de-escalation offers a novel bactericidal therapeutic alternative for high-inoculum, serious DNS MRSA infections.
Anti-Infective Research Laboratory, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, Michigan, USA.
Molly E
ME
Steed
Brian J
BJ
Werth
Cortney E
CE
Ireland
Michael J
MJ
Rybak
D017576:Daptomycin / Q000493:pharmacokinetics / Q000494:pharmacology*; D015194:Diffusion Chambers, Culture; D054796:Drug Dosage Calculations; D024901:Drug Resistance, Multiple, Bacterial / Q000187:drug effects; D004359:Drug Therapy, Combination; D004697:Endocarditis, Bacterial / Q000188:drug therapy* / Q000382:microbiology; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000254:growth & development; D008826:Microbial Sensitivity Tests; D008955:Models, Cardiovascular; D013203:Staphylococcal Infections / Q000188:drug therapy* / Q000382:microbiology; D015662:Trimethoprim, Sulfamethoxazole Drug Combination / Q000493:pharmacokinetics / Q000494:pharmacology*
D015662:Trimethoprim, Sulfamethoxazole Drug Combination; D017576:Daptomycin