Ceftazidime-avibactam Versus Tigecycline for the Treatment of Carbapenem-resistant Klebsiella Pneumoniae-induced Pneumonia in Critically Ill Patients

Background: To assess the safety patterns and outcomes of ceftazidime-avibactam (CAZ-AVI) versus tigecycline (TGC) for the treatment of carbapenem-resistant Klebsiella pneumoniae (CRKP) pneumonia dened as either hospital-acquired pneumonia (HAP) or ventilator-associated pneumonia (VAP). Methods: Clinical and microbiological cure rates, 28-day survival rates, and safety evaluation were compared between patients treated with CAZ-AVI versus those treated with TGC in a retrospective study. Conventional multivariate logistic regression analysis and three propensity score (PS) analyses were performed to control for confounding variables. Results: A total of 105 cases were included in the study; 62 patients (59%) received TGC, and 43 patients (41%) received CAZ-AVI. Clinical cure rates and microbiological cure success of CAZ-AVI were superior to TGC [51.2% versus 29.0%(P=0.022) and74.4% versus 33.9% (cid:0) P<0.001 (cid:0) , respectively]. There were no signicant differences between the two groups with regard to 28-day survival rates (66.1% versus 69.8%, P=0.695). In analyses of conventional multivariate logistic regression and propensity score (PS) analysis, patients in the CAZ-AVI group were more likely to have achieved clinical cure and microbiological success compared with patients in the TGC group. However, the difference between the two groups with regard to 28-day survival rates were not signicant. In terms of safety evaluation, generally, the CAZ-AVI group had a lower incidence of adverse reactions when compared with the TGC group. Conclusions: CAZ-AVI may be a suitable alternative to TGC for the treatment of HAP or VAP caused by CRKP in critically ill patients. bacilli by inhibiting carbapenemases without affecting the activity of ceftazidime (17, 18). Although certain studies have demonstrated the effectiveness and safety of Ceftazidime-avibactam (CAZ-AVI), and shown that it is superior to colistin for the treatment of CRE in vivo (14, 15), there is still considerable uncertainty regarding the optimal clinical treatment when comparing the outcomes of CRKP-infected HAP or VAP patients treated with CAZ-AVI to those treated with TGC (19, 20). The aim of the present study was to assess the safety patterns and outcomes of CRKP dened as either HAP or VAP in patients treated with either CAZ-AVI or TGC. The additional antibacterial drugs were not effective against the K. pneumonia that grew in the respiratory secretions. VAP/HAP episodes that were either isolated or in conjunction with mixed microorganisms and multi-site infection were included in the present study. broad-spectrum activity, linear pharmacokinetics with a high degree of lung penetration, and low risk of serious adverse events(36). Previous studies have shown the ecacy of CAZ-AVI in the treatment of infections due to CRE infection including CRKP (14, 20, 28, 37). Microbiological failure and crude mortality rates of pneumonia were 26.3% and 35.7% with adjusted analysis showing CAZ-AVI may be an important alternative for the treatment of KPC-Kp pneumonia (OR 6.73; 95% CI 1.39–34.94; P = 0.02) (38). Of importance, examination of the comparative effectiveness between polymyxin B and CAZ-AVI showed that all-cause 30-day hospital mortality and other clinical outcomes were improved in patients treated rst with CAZ-AVI (14). Sousa A. et al showed that CAZ-AVI was a promising salvage therapy for the treatment of OXA-48-producing Enterobacteriaceae with a 14% mortality rate after 14 days and a 10% recurrence rate after 90 days, even in monotherapy(39). The clinical cure of CAZ-AVI in our study was 51.2% and microbiological cure success was 74.4%. Clinical cure at the test-of-cure visit was achieved by 68.8% of CAZ-AVI recipients in the clinically modied intent-to-treat population, and by 77.4% in the clinically evaluable population from data of phase III REPROVE trial(40). Recently, a study from Tsolaki et al showed that patients with CAZ-AVI had improved clinical cure rates (80.5%), microbiological eradication (94.3%) and 28-day survival rates (85.4%) than those with other available antibiotic agents(41). It is hypothesized that these variations are primarily due to all the patients in the present study having HAP/VAP, higher Charlson’s comorbidity scores, more complicated risk factors for multisite infections and a greater risk of mortality. in clinical isolates were not routinely achieved by PCR and the combined medication regime did not monitor the in vitro synergistic sensitivity. Penetration into the bronchial ELF by CAZ-AVI and TGC in intrapulmonary pharmacokinetic and pharmacodynamics study shows that the ratios of lung ELF and serum AUC or concentration were 0.3 and 0.76 in healthy adults respectively (53, 54). Thirdly, in our study, the CAV-AVI and TGC regimen were combinations of antibiotics, whether such combinations cover the wide range of bacteria involved in polymicrobial infections were underestimated. Finally, outside of randomized trials, all conclusions regarding the ecacy of CAZ-AVI versus TGC should be validated in sole site infections and in multiple centres. In conclusion, the present study rst revealed the clinical value of CAZ-AVI for the treatment of HAP/VAP caused by CRKP. The data showed the superiority of CAZ-AVI over TGC with regard to clinical cure rates, microbiological cure success and safety issues, although no statistical differences in the 28-day survival rate in the critically ill patients with clinically conrmed HAP/VAP were observed. Further larger randomized clinical trials are required to conrm or exclude these observations.

Introduction least 4 mg/L (23). CRKP was resistant to most classes of antibiotics, except for TGC, polymyxins and CAZ-AVI. Escherichia coli (ATCC cat. no. 25922; ATCC) served as a laboratory quality control strain of MIC measurements. CRE colonization on respiratory tracts was identi ed by the patient's chest radiograph and laboratory examinations.
TGC-based and CAZ-AVI-based therapy excluded TGC and CAZ-AVI combination regime. In our centre, generally, TGC was administered intravenously with a 200 mg loading dosage, followed by a twice-daily maintenance dosage. The dosage of TGC was adjusted for alterations in liver function using the pharmaceutical direction. CAZ-AVI (2 g CAZ and 500 mg AVI) was given by 2 h intravenous infusions every 8 h. Patients with CRRT received a standard dosing for the adequacy of treatment. The dosage of CAZ-AVI was adjusted according to creatinine clearance (CLcr).

Outcome measurements
Clinical success was de ned as the normalization of non-microbiological indicators (such as radiological examinations and laboratory tests) or resolution in clinical symptoms (such as respiratory secretions volume and signs of fever) (19). Microbiological cure success was de ned as culture-con rmed eradication of the pathogen; no pathogen growth in the nal cultured specimen during the entirety of the hospital stay. Progressive or persistent symptoms and signs of infection, emergence of new episodes following active therapy and addition of other antibacterial treatments for the disease were considered clinically ineffective (24). If the patient's symptoms and signs disappeared, such that cultivable material was not available, the bacteriological results were presumed to be clear. The statistical clearance and hypothetical clearance of bacterial clearance were combined to calculate the clearance rate. Bacteriological failure was de ned by persistence of K. pneumonia isolates (1x10 5 CFU/ml for ETAs; 1x10 4 CFU/ml for BALF) on the follow-up cultures of the respiratory specimen.

Statistical analysis
Continuous variables were compared using a Student's t-test, Mann-Whitney U test or a Wilcoxon's rank sum test. Categorical variables were compared using a χ 2 test or a Fisher's exact test. A binary logistic regression was used to identify factors associated with clinical cure, microbiological success and 28-day survival rates.
Meaningful variables based on clinical judgment, and other variables with P < 0.10 in the univariate analyses, were included in the multivariate analysis. To prevent multicollinearity, certain factors were excluded from the multivariate analysis. Model discrimination was assessed using the area under the receiver operating characteristic curve (AUC), and model calibration was assessed using a Hosmer-Lemeshow test.
In addition, propensity score (PS) analysis was performed to control for confounding variables. PS was estimated using multivariate logistic regression analysis of several covariates (25) . The primary PS method was PS regression adjustment. The PS was an additional covariate in the binary logistic regression model. In the other methods of PS analysis, PS matching was performed, with a variable ratio of 1:2 based on a matching caliper of 0.2 on the PS scale. The balance of covariates between the two groups was evaluated by the standardized differences (< 0.20: good balance for a particular covariate). Finally, inverse probability of treatment weighting (IPTW) was used to adjust for confounding variables. A weighting logistic regression model was built using the stabilized IPTW weight, which was calculated by PS. Odds ratios (ORs) and 95% con dence intervals (CIs) were calculated to assess the relative risk of clinical outcomes. All tests of signi cance reported were two-tailed, and a P < 0.05 was considered to indicate a statistically signi cant difference. Statistical analyses were performed using SPSS version 22.0 (IBM, Corp), with a R2.15.X-psmatching 3.04 plug-in [Empower (R); empowerstats.com, X&Y solutions, Boston, Massachusetts, USA) and R(26, 27).

Patients
According to inclusion criteria, a total of 114 patients in the ICU were diagnosed with HAP or VAP caused by CRKP, and were treated with CAZ-AVI-based therapy or TGC-based therapy; 9 cases were excluded from the study, as they received a combination of CAZ-AVI and TGC therapy. Finally, 105 cases were included in the nal analyses; 62 patients (59%) received TGC-based therapy, and 43 patients (41%) received CAZ-AVI-based therapy.
The baseline clinical characteristics of the patients are as follows (Table 1): There were no signi cant differences with regard to age, comorbidities, severity of illness scores, CRRT, VAP and concurrent multisite infections between the two groups. There were statistical differences in sex, and monotherapy between the two groups, CAZ-AVI group included more male patients and monotherapy treatment options.

Evaluation of clinical outcomes
The data of the two groups were processed using a multivariate regression model and PS analyses, so as to further analyse whether there were differences in terms of clinical e cacy, microbiological clearance and 28-day survival. Table 1 shows the clinical outcomes of the study patients. The clinical cure rate was 51.2% (22/43) in the CAZ-AVI group, and 29.0% (18/62) in the TGC group (P = 0.022). The rate of microbiological cure success was 74.4% (32/43) in the CAZ-AVI group and 33.9% (21/62) in the TGC group (P < 0.001). There were no signi cant differences between the two groups with regard to the 28-day survival (66.1% vs. 69.8%, P = 0.695). Table 2, a multivariate analysis model indicated that CAZ-AVI use, age and the SOFA score at onset of infection were independently associated with clinical cure rates. In the multivariate analysis model of microbiological cure success, CAZ-AVI use was an independent factor in the analysis model. SOFA score at onset of infection was a signi cant prognostic factor for the 28-day survival rate. Conversely, CAZ-AVI use was not signi cantly associated with a decreased 28-day survival rate.

As shown in
PS was derived from the multivariate logistic regression analyses of the covariates (sex, age, comorbidities, Charlson's score, VAP, CRRT, SOFA score at onset of infection, APACHE II score at onset of infection and monotherapy). PS regression adjustment was used as the primary PS method; CAZ-AVI use and PS (derived from the aforementioned covariates) were included in the binary logistic regression model in order to calculate the OR of clinical cure. The ORs (95% CI) for use of CAZ-AVI according to the PS regression adjustment model are shown in Table 3. Patients who had used CAZ-AVI were more likely to have achieved a clinical cure (OR, 3.405; 95% CI, 1.304-8.889) and microbiological success (OR, 7.778; 95% CI, 2.717-22.265) than patients who used TGC. However, there was no statistical signi cance between two groups with regard to 28-day survival rates.
As shown in Table 4, a total of 75 patients (30 in the CAZ-AVI group and 45 in TGC group) were included in the 1:2 variable ratio PS matched cohort. In the matched analytic sample, the differences between the two groups were attenuated (absolute standardized difference < 0.20). Clinical cure rates were 53.3% (16/30) in the CAZ-AVI group and 22.2% (10/45) in the TGC group. The rate of microbiological success was 73.3% (22/30) in the CAZ-AVI group and 28.9% (13/45) in the TGC group. Patients of the CAZ-AVI group were more likely to have achieved a clinical cure and microbiological success than patients of the TGC group (OR, 4.000; 95% CI, 1.446-11.064 and OR, 7.310; 95% CI, 2.510-21.286, respectively). Similarly, there was no signi cant difference between the two groups with regard to the 28-day survival rates. In addition, IPTW yielded similar results (Table 3).

Safety evaluation
The safety of CAZ-AVI or TGC in this study was evaluated from four aspects: Liver function [alanine transaminase (ALT), total bilirubin(TBil)]; renal function [serum creatinine(Scr)]; coagulation function [activated partial thromboplastin time (APTT), brinogen(Fib)]; other adverse reactions (the most prominent adverse reaction observed in this study were diarrhoea). Differences in the TBil, Fib or APTT values before and after treatment in TGC group were all statistically signi cant (P < 0.001; Table 6). By contrast, there was no marked difference in these indices before and after treatment in the CAZ-AVI group. The index differences of the two groups before and after treatment (Δ) was used to re ect the differences of the two drugs treatment. As shown in Table 5, there were statistically signi cant differences in ΔTBil, ΔFib and ΔAPTT between the TGC and CAZ-AVI groups. The only prominent adverse reaction observed in the present study was diarrhoea. In the TGC group, 27.4% (17/62) of cases developed diarrhoea during the treatment period, whereas only 7.0% (3/43) of cases had diarrhoea in the CAZ-AVI group (P = 0.009).

Discussion
To the best of our knowledge, the present study is the rst to compare the effectiveness of CAZ-AVI and TGC for the clinical treatment of critically ill patients with HAP/VAP due to CRKP infection. The primary nding from this retrospective cohort study was that CAZ-AVI use was an independent factor in the conventional multivariate analysis of clinical cure and microbiological success. The clinical cure rates and microbiological success in the CAZ-AVI group were signi cantly higher than those of the TGC group after PS analysis, but there was no statistical differences in 28-day survival rates in the critically ill patients two treatment regimens. Several previous reports of CRE infections treated with CAZ-AVI based combination regimes similarly reported favourable outcomes in these patients (15,19,28). Additionally, safety evaluation between TGC and CAZ-AVI showed that TGC regime was associated with a greater occurrence of adverse reactions, including liver injury, coagulation disorder and diarrhoea.
Of note, the increase in antimicrobial resistance has encouraged the identi cation of novel antibiotics, such as meropenem/vaborbactam and plazomicin, although high prices and non-attainable precluded assessment for novel Gram-negative antibiotics in clinical practice has hampered their applicability. TGC has not been approved for the treatment of HAP or VAP, due to its inferiority compared with the imipenem/cilastatin regimen in HAP patients, and the increased mortality rates in the group of patients with VAP treated with standard dose of TGC (50 mg every 12 h; loading dose 100 mg) (29). However, favourable responses with a high TGC dose (200 mg followed by 100 mg every 12 h) has been shown amongst patients with severe systemic infections, with di cult to treat MDR or XDR Gram-negative bacteria (16, 30). As for CRKP infections, the cure rates of high-dose TGC in other studies was 34.6% (31) and 80% (32) in mixed infections, and 47.8% in bloodstream infections (33), all of which are higher than the results of the present study (29%). This may be explained by the different sites of infection. Since there are no previous studies speci cally addressing the role of CRE in HAP/VAP, like-for-like comparisons with previous studies cannot be made. HAP caused by CRE is associated with a signi cantly higher infection-related mortality rate compared with CRE infections at other sites (61.4% versus 34.6%) (34). Accordingly, microbiological eradication rates of high dose TGC for CRKP has been widely reported, and they range from 31.2%-66.7% (32,35), which are higher than that observed in the present study.
CAZ-AVI, a promising option for the treatment of carbapenem resistant Gram-Negative pathogens (excluding Acinetobacter baumannii and Stenotrophomonas maltophilia), has been approved by the U.S. FDA and European Medicines Agency for the treatment of HAP/VAP for its attractive bactericidal broad-spectrum activity, linear pharmacokinetics with a high degree of lung penetration, and low risk of serious adverse events(36). Previous studies have shown the e cacy of CAZ-AVI in the treatment of infections due to CRE infection including CRKP (14,20,28,37). Microbiological failure and crude mortality rates of pneumonia were 26.3% and 35.7% with adjusted analysis showing CAZ-AVI may be an important alternative for the treatment of KPC-Kp pneumonia (OR 6.73; 95% CI 1.39-34.94; P = 0.02) (38). Of importance, examination of the comparative effectiveness between polymyxin B and CAZ-AVI showed that all-cause 30-day hospital mortality and other clinical outcomes were improved in patients treated rst with CAZ-AVI (14). Sousa A. et al showed that CAZ-AVI was a promising salvage therapy for the treatment of OXA-48-producing Enterobacteriaceae with a 14% mortality rate after 14 days and a 10% recurrence rate after 90 days, even in monotherapy (39). The clinical cure of CAZ-AVI in our study was 51.2% and microbiological cure success was 74.4%. Clinical cure at the test-of-cure visit was achieved by 68.8% of CAZ-AVI recipients in the clinically modi ed intent-to-treat population, and by 77.4% in the clinically evaluable population from data of phase III REPROVE trial (40). Recently, a study from Tsolaki et al showed that patients with CAZ-AVI had improved clinical cure rates (80.5%), microbiological eradication (94.3%) and 28-day survival rates (85.4%) than those with other available antibiotic agents (41). It is hypothesized that these variations are primarily due to all the patients in the present study having HAP/VAP, higher Charlson's comorbidity scores, more complicated risk factors for multisite infections and a greater risk of mortality.
Inappropriate doses of antimicrobial agents may also lead to treatment failure or drug resistance of pathogens in critically ill patients who receive renal replacement therapy. No signi cant in uence of CRRT on the pharmacokinetics of TGC has been found, considering their non-renal elimination (42). Shields et al showed that CRRT are risk factors for CAZ-AVI treatment failure amongst patients with CRE infections; whereas, adequate doses of CAZ-AVI when 46.5% patients received continuous venovenous hemodia ltration guaranteed a 100% fT > 4MIC of CAZ as described in a previous case report(28, 43). However, pharmacokinetic and PK/PD studies are required for lung infections, as drug concentrations in the intracellular epithelial lining uid were important for the treatment of "resistant" pathogens.
Understanding the speci c types of carbapenemases produced by a CRE clinical isolate is very important for the choice of drug treatment. CRE includes heterogeneous pathogens with multiple potential resistance mechanisms, which are roughly divided into pathogens that produce carbapenemases and those that do not. Avibactam is similar in activity against SHV-4 as clavulanic acid and anti-CTX-M-15 with clavulanic acid and tazobactam, but more potent against KPC-2 producing carbapenemases and Class C β-lactamase (44)(45)(46). If a metallo-β-lactamase [such as the New Delhi metallo-β-lactamase 1(NDM), Verona integrin-encoded] is identi ed, antibiotic options would be preferred to CAZ-AVI plus aztreonam for good clinical treatment (47,48). The most notable difference between CAZ-AVI and TGC was that the activity of TGC against CRE is independent of the presence or type of carbapenemases. Currently 97.4% of clinically isolated CRE strains in China primarily produce bla KPC−2 (51.6%) and bla NDM (35.7%) and bla OXA−48−like carbapenemases (7.3%), whereas minor strains carry bla IMP and several carbapenemases. Overall, 64.4% of K. pneumoniae were bla KPC−2 producers and 21.1% were NDM producers (including 9.0% bla NDM−1 producers, 12.0% bla NDM−5 producers and 0.1% bla NDM−3 producers), with few differences between various epidemiological studies (5,49). Therefore, from the point of the mechanism of resistance, CAZ-AVI had a 20% higher failure rate in the treatment of CRE infection than TGC, but the present study still showed favourable clinical cure (OR, 3.405; 95% CI, 1.304 to 8.889) and microbiological cure success (OR, 7.778; 95% CI, 2.717 to 22.265) with fewer adverse reaction.
In the present study, there were notable differences in the rates of adverse events observed between CAZ-AVI and the TGC group. Although high-dose TGC has better e cacy and tolerability (30), nausea and vomiting were common adverse events. The primary concern associated with a high dose of TGC remains the reported safety problems. More recently, severe coagulopathy with hypo brinogenemia associated with the use of high-dose TGC has gained increasing attention (50,51). In addition, TGC-induced liver toxicity has been reported previously (35,52); however, the relationship remains unclear. In the present study, the effects of pre-treatment TBil levels were adjusted for, and it was found that TGC induced an increase in TBil. Another prominent adverse reaction observed in this study was that 27.4% patients treated with a high-dose of TGC suffered diarrhoea, similar to the rate (34.3%) of the study by Chen et al. (35). In contrast, there were no differences with regard to kidney, liver and coagulation indices and diarrhoea before and after CAZ-AVI treatment, thus con rming the safety pro le of CAZ-AVI observed in previous studies (19,20,38).
The present study is limited by its retrospective, small clinical sample size and single-centre observational design, which could not exclude indication biases. Additionally, de nitive identi cation of carbapenemases in clinical isolates were not routinely achieved by PCR and the combined medication regime did not monitor the in vitro synergistic sensitivity. Penetration into the bronchial ELF by CAZ-AVI and TGC in intrapulmonary pharmacokinetic and pharmacodynamics study shows that the ratios of lung ELF and serum AUC or concentration were 0.3 and 0.76 in healthy adults respectively (53,54). Thirdly, in our study, the CAV-AVI and TGC regimen were combinations of antibiotics, whether such combinations cover the wide range of bacteria involved in polymicrobial infections were underestimated. Finally, outside of randomized trials, all conclusions regarding the e cacy of CAZ-AVI versus TGC should be validated in sole site infections and in multiple centres.
In conclusion, the present study rst revealed the clinical value of CAZ-AVI for the treatment of HAP/VAP caused by CRKP. The data showed the superiority of CAZ-AVI over TGC with regard to clinical cure rates, microbiological cure success and safety issues, although no statistical differences in the 28-day survival rate in the critically ill patients with clinically con rmed HAP/VAP were observed. Further larger randomized clinical trials are required to con rm or exclude these observations. Declarations This study was supported by"Youth Medical Talent" Project in Jiangsu Province (QNRC2016557) and"Six One Project"Research Project for High-level Talents in Jiangsu Province (LGY2019067).

Availability of data and materials
All data generated or analysed during this study are included in this published article.
Ethics approval and consent to participate Informed consent was obtained from patients' parents.

Consent for publication
Not applicable.

Competing interests
The authors declare that they have no competing interests.     b: Data are presented as the median (interquartile range).
c: Δ was de ned as differences between the index before and after the use of TGC or CAZ-AVI.