Etiologic analysis of Chinese patients with agranulocytosis and hematopathies infected with resistant bacteria : Anti-bacterial effect of tigecycline

Purpose: To assess the etiologic characteristics of resistant bacterial infections occurring in agranulocytosis patients with hematopathies, and to determine the effect of tigecycline (TGC). Methods: After ineffective treatment with carbapenem, all of the patients were divided into the following three groups: TGC alone (15 cases); TGC as initial treatment, followed by a combination with other antibiotics (40 cases); and TGC in combination with other antibiotics from the start of treatment (71 cases). Results: Among the 126 patients, 108 had fevers (85.71 %). The most common infection site was lung, accounting for 71.43 % of all infections. A total of 52 pathogens were isolated from 126 hospitalized patients, including 38 Gram-negative bacteria (70.37 %), 14 Gram-positive bacteria (25.93 %), and 2 fungi (3.70 %). TGC treatment efficacy was 50.79 %. There were no statistically significant differences between the three treatment groups (p = 0.473). Adverse drug reaction was nausea and vomiting (14.29 %), nausea without vomiting (11.90 %), diarrhea (6.35 %), and generalized skin rash with itching (3.17 %). Conclusion: TGC is effective in treating neutropenic patients with hematopathies who are infected with resistant bacteria. The side effects of TGC are few; thus, TGC is safe and generally well-tolerated.


INTRODUCTION
After treatment with different chemotherapy regimens, patients with hematologic malignancies may show varying degrees of bone marrow suppression, immunosuppression, intestinal mucosal barrier damage [1], and risk of infections.Immunosuppression, using broadspectrum antibiotics, and immunosuppressants are usually correlated with an increased appearance of antibiotic-resistant bacteria [2].There has been a significant increase in the incidence of multi-resistant microorganisms, which were the main causes of death in patients with hematological malignancy [3,4].As the effect of bacterial cultures is low and timeconsuming, the introduction of empiric antibiotic therapy to prevent and control infections in the early stages is important to improve the survival rate of patients with hematopathies.Tigecycline (TGC) is the first available antimicrobial agent in a new class of antimicrobials, which was called TGCes, which are structurally similar to tetracyclines.Compared with tetracycline, TGC provides a broader antimicrobial spectrum and lower susceptibility to resistance development with the special structure by itself.TGC offers a broader anti-microbial spectrum and a lower susceptibility for the occurrence of resistance than tetracyclines.TGC has an activity against of multiple drug resistance (MDR) bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), and extended-spectrum beta-lactamaseproducing Enterobacteriaceae (ESBL), Klebsiella pneumoniae, carbapenemase-producing Klebsiella pneumoniae (KPC-Kp), and the Acinetobacter baumannii group [5].TGC has been licensed for the treatment of complicated intra-abdominal infections (cIAIs), complicated skin and soft tissue infections (cSSTIs), and communityacquired pneumonia (CAP).There are limited reports on the use of TGC in patients with granulocytosis with drug-resistant bacterial infections.
Based on recent studies, TGC has several advantages: (a) TGC's broad-spectrum activity includes gram-positive, gram-negative, anaerobic and atypical pathogens, except for Pseudomonas aeruginosa, Proteus mirabilis, Mortierella molhid and Providencia.TGC also has a broad spectrum of activities, including MDR/XDR Gram-positive and negative bacteria, with the exception of Pseudomonas.[15][16][17].(b) Because of the special structure, TGC meets the urgent need to overcome the deteriorating antimicrobial drug resistance by overcoming ribosomal protection and effective drug efflux resistance mechanisms [18].(c) Lower liver and kidney toxicity for patients complicated by liver or kidney disease.(d) The side effects are welltolerated.
TGC is a safe and efficacious antibiotic for treating infections caused by XDR or MDR bacteria; however, few studies have systemically investigated the benefits resulting from TGC treatment in neutropenic adult patients with hematopathies infected with resistant bacteria.A retrospective study of a TGC-based treatment approach was performed to analyze the curative effect and safety of TGC to treat agranulocytosis patients suspected to have resistant bacterial infections.

Study design
The medical records of agranulocytosis patients with resistant bacterial infections, who were treated in the Hematology Department of Sichuan People's Hospital (ChengDu, China) between October 2010 and October 2015 were retrospectively reviewed.This study was approved by the Ethics Committee of Sichuan Academy of Medical Science and Sichuan People's Hospital for Human Research in accordance with International ethical guidelines for biomedical research involving human subjects [19] and Declaration of Helsinki promulgated in 2013 (Ethical review(research) No. 25,2015) [20].

Clinical data collection
Consecutive patients of any age with hematopathies who were admitted with neutropenia and documented cultures of resistant bacteria were enrolled in the study.Access to clinical data including age, gender, underlying disease, severity of neutropenia, presence of central venous catheters, organisms isolated from the blood and antimicrobial susceptibility, administration of antibiotics, efficacy and safety.

Bacteriologic identification and antimicrobial susceptibility evaluation
Culture samples were obtained from the peripheral blood, catheter blood, and other sites of infection.Disk diffusion technology is used for bacterial identification.Sensitivity tests were performed using the Microscan system (Dade Behring, West Sacramento, CA, USA) and the results were interpreted according to the CLSI guidelines published in 2012 [6].

Definitions
Fever is defined as the mouth temperature of 38.3 ° C or the mouth temperature of 38 ° C for 1 hour [7].Neutropenia was defined as an absolute neutrophil count (ANC) < 500/mm 3 or < 1000/mm 3 and was expected to drop to < 500/mm 3 within 2-3 days.Severe neutropenia was defined as ANC < 100/mm 3 [8,9].Multi-drug resistant (MDR) was diagnosed when no susceptibility to no less than three antimicrobial categories.
According to the consensus of European experts, extensive resistance (XDR) is defined as resistance to not less than one agent but up to two classes of antimicrobial agents [10].Bloodstream infection (BSI) was considered, when it was hospital-acquired, healthcarerelated, according to the criteria described previously [11].The catheter-related bloodstream infection (CRBSI) was considered to be a bloodstream infection in patients with intravascular catheters or catheter removal within 48 hours, with fever, chills or hypotension and no other source of infection.

Treatment
After ineffective treatment with a carbapenem antibiotic, all of the patients were treated with TGC for resistant bacterial infections and concurrent granulocytopenia, and divided into three groups according to the drug regimen: TGC alone (15 cases); TGC as initial treatment, followed by a combination with other antibiotics (40 cases); and TGC in combination with other antibiotics from the start of treatment (71 cases).
TGC was administered intravenously (40-60 min drip infusion) at an initial dose of 100 mg and a maintenance does of 50 mg every 12h.The entire course of treatment was 5-7 days in length.When the body temperature was normal, step-down treatment was initiated or the drug was discontinued.

Clinical outcome
The clinical response was determined based on the investigator's judgement.They specified the success or failure of the treatment according to commonly used clinical practice criteria.When the symptoms and signs are completely relieved or improved, consider the clinical response chosen.The patient was cured or improved, and there was no need to change treatment regimen.
A lack of serious adverse effects leading to discontinuation of treatment could also be considered as a favorable clinical response.When the clinical signs and symptoms of infection persist or worsen, or when new signs or symptoms were acquired.Therefore, another class of antibiotic was added to the treatment regimen or there was a change to an alternative antibiotic regimen.

Statistical analysis
Statistical analyses were primarily descriptive using a χ 2 test.P < 0.05 was considered statistically significant.All data were analyzed using SPSS (version 16.0; SPSS, Inc., Seoul, Korea).

Patient characteristics
A total of 126 patients (62 females and 64 males) who were infected with resistant bacteria and treated with TGC were documented.Table 1 lists the baseline characteristics of patients.All patients showed neutropenia at time of infection.Number of male and female was almost equal.Most patients with neutropenia suffer from acute myeloid leukemia (83.3 %).Central venous catheters (100 %), high-dose chemotherapy (28.57%), immune-suppressive therapy (15.08 %), and diabetes mellitus (15.08 %) were the 4 main reasons for infection with resistant bacteria in the 126 patients.Among the 126 patients, 108 had fevers (85.71%), and the most common infection site was the lung (71.43 %).

Microbiologic activity
Fifty-four strains of bacteria were obtained from 126 hospitalized neutropenic patients with hematopathies.The majority of strains 38 of 54 (70.37 %) were Gram-negative bacteria.The most commonly found Gram-negative andpositive organisms were Enterobacteriaceae and staphylococci (CoNS), respectively.We also observed 2 fungi (3.70%).The pathogens and the frequencies were shown in Table 2.

TGC administration
TGC was used according to the manufacturer's instructions with an initial dose of 100 mg and then 50 mg every 12 hours.Despite the use of broad-spectrum antibiotics, all patients with persistent fever or worsening signs of infection were treated with TGC.TGC was used for 10 days (range 1-28 days).Fifteen patients received TGC monotherapy, 40 patients received TGC as initial treatment followed by combination with other antibiotics, and 71 patients received TGC combined with other antibiotics from the start of treatment.The antibiotic therapy regimens are listed in Table 3.

Response and duration of therapy
The TGC response rates are shown in Table 4.Among 64 (50.79 %) patients, the TGC treatment was successful.The median duration in the patients with good responses to the TGC treatment till defervescence was 2.13 days (range, 0-6 days).There was no significant difference in the efficacy of TGC monotherapy and combination therapy (p = 0.473), though it appeared to be a trend that it was more efficacy when TGC was administrated alone (66.67 % vs. 48.6 %), which is in contrast with recent studies.The possible reason for this finding is the small sample size that caused incorrect results.Importantly, there was a significant difference in response rates between the two combination treatment groups (20/40 {50 %} vs. 34/71 {47.89 %}; p = 0.900), although there appeared to be a trend towards more efficacy of initial treatment, followed by the combination group more so than the combination treatment from the start group.

Toxicity during TGC therapy
Toxicity data were shown in Table 5. Toxicity induced by TGC therapy occurred in 45 (35.7 %) patients.Grade 3 toxicity occurred in 1 of 9 patients (7.14 %).The main toxicities were nausea with vomiting (14.29 %), nausea without vomiting (11.90 %), diarrhea (6.35 %), and systemic skin rash with itching (3.17 %).All of the adverse side effects resolved after discontinuing TGC.Organ toxicity involving the kidneys and liver was noted in accordance with the drug metabolism process.

DISCUSSION
Even though new and exciting developments have been achieved recently, the main treatment and pathophysiologic characteristics have caused neutropenia in patients with hematopathies.The resulting neutropenia results in morbidity and mortality in patients with hematological disorders.The mortality rates in neutropenic patients with hematopathies and concurrent resistant bacterial infections were very high before the advent of the antibiotic era.The treatment of neutropenic patients changed when empirical antibiotic therapy was introduced; however, the resistance to the antibiotic agents is the main problem that seriously influence the treatment effect on bacterial infections [12].To solve this problem, it is needed to develop a new broad-spectrum antibacterial agent.TGC was initially approved by the US FDA in June 2005 to indicate the treatment of complex skin, soft tissue, and intra-abdominal infections [13,14].A clinical retrospective study on the efficiency and safety of the TGC treatment as empirical antibiotic therapy was performed in study.First of all, the clinical features of neutropenic patients with resistant bacterial infections were detected.The results showed that neutropenia usually occurs in patients with hematological malignancies, which is the result of enhanced myelosuppressive chemotherapy.The risk factors for neutropenic adult patients with hematopathies infected with resistant bacteria include intensive chemotherapy, use of central venous catheters, immunosuppression, and diabetic complications.Neutropenia resulting from intensive chemotherapy increases the risk of bacterial infections and repeated central venous catheterization increases the risk of exogenous infections.Immunosuppressive agents can reduce the proliferation and function of immune cells, resulting in weakening of the immune response, and thus increasing the risk of infection.Patients with diabetes mellitus have an underlying metabolic disturbance and significant reduction in disease-resistant ability [19,20].A fever was the major symptom of infection, accounting for 85.71 % of all cases.Bacteria induce the release of endogenous pyrogens, which can penetrate through blood-brain barrier and cause fever [21].Clinicians use physical therapy to control the body temperature and sensitive antibiotics to cure infections.Because of the special characteristics of the lung, pneumonia should be avoided in patients with hematopathies.There were some new drugs anti-Gram-positive infections, but the drugs for MDR Gram-negative infections that lead to the occurrence of an increased proportion of bacteremia, and the occurrence of MDR microorganisms were limited [22,23].In accordance with those results, our study showed that resistant Escherichia coli and Klebsiella pneumonia bacteremia were the two major pathogens in patients with hematologic malignancies [24].The cure rate of TGC treatment on the patients with bacteremia was 50.79 %, which is higher than a previous study [25].It was assumed that long-term use of carbapenem antibiotics before TGC was administered to patients who were not severely ill, which resulted in this finding.In the current study, there was no significant difference in the remission rate between the TGC monotherapy group and the combination therapy group.However, it shown a tendency to increase the effect of using TGC alone, reflecting the wrong sample size.
It is worth noting that there is still no significant difference between the two groups.Although there appeared to be a trend towards more efficacy than combination treatment from the beginning.In this regard, it would be interesting to perform a matched cohort analysis for comparing which kind of combination treatment was suitable for the treatment of MDR/XDRAB neutropenic patients with hematopathies.Inconsistent results have been reported with respect to the combination treatment effect for various MDR/XDRAB infections [26].The median duration of the group that had good responses to TGC was 2.13 days (range, 0-6 days), indicating that temperature was used as the main parameter to identify patients who were sensitive to TGC.There were some positive outcomes arising from this study.First, the main bacteria were identified which occurred in MDR/XDRAB neutropenic patients with hematopathies.Second, this efficiency is the first comparison between TGC, as initial treatment, followed by combination with other antibiotics and TGC in combination with other antibiotics and treatment.

Limitations
Some limitations existed in this study.First, it was a single-center, retrospective, and underpowered study.Second, it was not a matched cohort analysis, and the variations made our analysis complicated and not precise enough to provide evidence for clinical application.Third, few patients received TGC monotherapy for MDR/XDRAB.However, based on the primary analysis, it is difficult to attribute clinical and microscopic responses to TGC alone or in combination.

CONCLUSION
The results support the view that TGC shows good efficacy for MDR/XDRAB neutropenic patients with hematopathies without any severe side effects.Therefore, clinicians can use TGC as soon as carbapenem antibiotic treatment fails.In addition, due to the lack of high-level evidence of the superiority of combination therapy, TCG combination therapy may not be the main recommendation.
Therefore, meticulously designed studies are needed to evaluate the efficacy and safety of combination therapy compared with TGC monotherapy.

Table 1 :
Patient characteristics

Table 4 :
Cure rate (%) of TGC among three groups of agranulocytosis patients

Table 5 :
Toxicity of TGC treatment