In Vitro Activity of Various Antibiotics in Combination with Tigecycline Against Acinetobacter baumannii: A Systematic Review and Meta-Analysis.

Given that tigecycline-based combination therapy is recognized as a valuable option for the treatment of tigecycline-resistant Acinetobacter baumannii, we conducted this systematic review and meta-analysis to assess the overall evidence of its effectiveness. The synergy rate was defined as the primary outcome that was calculated separately for time-kill, Etest, and checkerboard microdilution methods. The secondary outcomes were bactericidal activity and the efficacy of combination treatment on the development of resistance. In total, 37 published papers and 16 conference proceedings were included. Nine classes consisting of 22 antibiotic types in combination with tigecycline against 1,159 A. baumannii strains were reported in the analysis. For the time-kill studies, combination therapy showed a synergy rate of 37.9% (95% confidence interval [CI], 30.7-46.5); the highest synergy rate was 67.4% (95% CI, 27.3-91.9) for tigecycline in combination with colistin. Moreover, combination with amikacin or colistin could efficiently inhibit the development of tigecycline resistance. Compared with checkerboard microdilution and Etest methods, time-kill studies always showed higher synergy rates. Altogether, these results suggest that the in vitro tigecycline-based combinations resulted in moderate synergy rates and that several combinations could suppress the resistance of A. baumannii to tigecycline, which should be further confirmed in animal models and clinical trials.