Objective:To investigate the clinical efficacy of injectable polymyxin B combined with tigecycline in pneumonia caused by pan-drug resistant Klebsiella pneumonia (PDR-KP). Methods:The retrospective analysis utilized clinical data of 71 patients with PDR-KP admitted to the Neurointensive Care Unit of Beijing Chaoyang Integrative Medicine Emergency Medical Center between September 2018 and August 2021. All patients received injectable polymyxin B combined with tigecycline. The response rate, bacterial clearance rate, and safety of this therapeutic option were evaluated according to the clinical symptoms and biochemical parameters before treatment (baseline), 7 days after the treatment, and at the end of the treatment.Results:The treatment time of 71 patients ranged from 8 to 14 days, with an average of 11 days. The symptoms, signs, laboratory tests, and chest CT findings of most patients significantly improved after the treatment using polymyxin B combined with tigecycline. On the 7th day after the treatment, 37 patients were clinically effective, with a total effective rate of 52.1%(37/71); 41 patients obtained bacteriological clearance, with a bacterial clearance rate of 57.7%(41/71). At the end of treatment, 51 patients were clinically effective, with a total effective rate of 71.8%(51/71); 56 patients obtained bacteriological clearance, with a bacterial clearance rate of 78.9%(56/71). Compared with the results on the 7th day after the treatment, the total effective rate ( χ2=5.86, P=0.016) and bacterial clearance rate ( χ2=7.32, P=0.007) of patients at the end of treatment were significantly increased. Skin pigmentation occurred in 39.4%(28/71) of patients during the treatment. Conclusions:Polymyxin B combined with tigecycline can be tried as a treatment option for pneumonia caused by PDR-KP, but more reliable clinical evidence is still needed.