Klebsiella pneumoniae is one of the most significant nosocomial pathogens in healthcare settings. Over the last decade, K. pneumoniae producing extended-spectrum β-lactamases (ESBLs) have been prevalent worldwide. ESBL-producing isolates are considered resistant to all penicillins, cephalosporins and aztreonam, and carbapenems are the only β-lactams that still remain consistently active.1 But owing to the overuse of carbapenems, resistant strains have become endemic in many countries as well. In addition, most carbapenem-resistant K. pneumoniae (CR-KP) are resistant to other antimicrobial classes, referred to as multidrug-resistant (MDR) and extensively drug-resistant strains.2 The lack of active antimicrobials against CR-KP continues to threaten public health.

Tigecycline is the first member of the glycylcycline class with high affinity to bacterial ribosomes and is unaffected by the typical resistance mechanisms of the tetracycline class.3 It has appealing in vitro activity against resistant Gram-negative bacteria including MDR Acinetobacter baumannii and carbapenem-resistant Enterobacteriaceae.3 But the concentrations of tigecycline in serum and pulmonary epithelial lining fluid are suboptimal, and long-term use may lead to resistance in vivo.4 Besides, randomized trials have indicated that the single use of tigecycline may confer an increased mortality risk.5 Therefore, for enhancing antibacterial activity and reducing resistance development, many physicians prefer to use antibiotic combinations that may act synergistically for treating infections caused by CR-KP.

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