The Comparative Efficacy of Colistin Monotherapy and Combination Therapy Based on in vitro Antimicrobial Synergy in Ventilator-associated Pneumonia Caused by Multi-drug Resistant Acinetobacter baumannii

Polymyxin combination therapy for multidrug-resistant, extensively-drug resistant, and difficult-to-treat drug-resistant gram-negative infections: is it superior to polymyxin monotherapy?

INTRODUCTION

The increasing prevalence of infections with multidrug-resistant (MDR), extensively-drug resistant (XDR) or difficult-to-treat drug resistant (DTR) Gram-negative bacilli (GNB), including Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae, Enterobacter species, and Escherichia coli poses a severe challenge.

AREAS COVERED

The rapid growing of multi-resistant GNB as well as the considerable deceleration in development of new anti-infective agents have made polymyxins (e.g. polymyxin B and colistin) a mainstay in clinical practices as either monotherapy or combination therapy. However, whether the polymyxin-based combinations lead to better outcomes remains unknown. This review mainly focuses on the effect of polymyxin combination therapy versus monotherapy on treating GNB-related infections. We also provide several factors in designing studies and their impact on optimizing polymyxin combinations.

EXPERT OPINION

An abundance of recent in vitro and preclinical in vivo data suggest clinical benefit for polymyxin-drug combination therapies, especially colistin plus meropenem and colistin plus rifampicin, with synergistic killing against MDR, XDR, and DTR P. aeruginosa, K. pneumoniae and A. baumannii. The beneficial effects of polymyxin-drug combinations (e.g. colistin or polymyxin B + carbapenem against carbapenem-resistant K. pneumoniae and carbapenem-resistant A. baumannii, polymyxin B + carbapenem + rifampin against carbapenem-resistant K. pneumoniae, and colistin + ceftolozan/tazobactam + rifampin against PDR-P. aeruginosa) have often been shown in clinical setting by retrospective studies. However, high-certainty evidence from large randomized controlled trials is necessary. These clinical trials should incorporate careful attention to patient's sample size, characteristics of patient's groups, PK/PD relationships and dosing, rapid detection of resistance, MIC determinations, and therapeutic drug monitoring.

Polymyxin Monotherapy vs. Combination Therapy for the Treatment of Multidrug-resistant Infections: A Systematic Review and Meta-analysis

Objectives

The objective of this review was to compare the effectiveness of Colistin monotherapy and combination therapy for the treatment of multidrug-resistant gram-negative bacterial infections.

Data sources

PubMed, Cochrane Library.

Study eligibility interventions and exclusions

In this systematic review, we included all retrospective and prospective studies and randomized controlled trials (RCTs) that compared intravenous polymyxin monotherapy and combination therapy with any other antibiotic for treating multidrug-resistant infections. Studies using inhaled polymyxins with 5 or less than 5 patients were excluded. The primary outcome was 30-day all-cause mortality and if not reported at day 30 we extracted and documented the closest time point. Both crude outcome rates and adjusted effect estimates were extracted for mortality.

Study appraisal data extraction and synthesis

Search string used was "(Colistin OR polymyxin) AND (Enterobacteriaceae OR Klebsiella OR Acinetobacter OR Escherichia coli OR Pseudomonas) AND (random OR prospective OR retrospective OR cohort OR observational OR blind)." Thirty-nine studies were included in our analysis; out of which 6 RCTs were included and 9 studies used carbapenem as the adjunctive antibiotic. Each study was screened and reviewed for eligibility independently by two authors and data extrapolated on an Excel sheet.

Results

The meta-analysis of polymyxin monotherapy vs. combination therapy in multidrug-resistant infections yielded an odds ratio (OR) of 0.81 (95% confidence interval [CI]: 0.65-1.01) with minimal heterogeneity (I ² = 40%), whereas pooled analysis of this comparison in studies that included carbapenem as combination therapy yielded an OR of 0.64 (CI: 0.40-1.03; I ² = 62%). Likewise, the pooled analysis of the RCTs yielded an OR of 0.82 (95% CI: 0.58-1.16, I ² = 22%). All these showed no statistical significance. However, it was seen that polymyxin combination therapy was more effective in multidrug-resistant infections compared to polymyxin monotherapy. The effectiveness was more glaring when carbapenems were used as the combination drug instead of any other antibiotic and more so in many in vitro studies that used polymyxin combination therapy.

Conclusion

Although statistically insignificant, it would be prudent to use polymyxin combination therapy to treat multidrug-resistant gram-negative bacilli (GNB) infection over monotherapy with preference to use carbapenem as the adjunct alongside polymyxins.

How to cite this article

Samal S, Mishra SB, Patra SK, Rath A, Dash A, Nayak B, et al. Polymyxin Monotherapy vs. Combination Therapy for the Treatment of Multidrug-resistant Infections: A Systematic Review and Meta-analysis. Indian J Crit Care Med 2021;25(2):199-206.

Is colistin-associated acute kidney injury clinically important in adults? A systematic review and meta-analysis

Colistin is the last-resort antimicrobial agent against infections caused by multidrug-resistance Gram-negative bacteria (MDR-GNB). However, a differing risk of colistin-associated acute kidney injury (CA-AKI) has been demonstrated without affecting mortality, thus the association and its importance needs to be questioned. To assess the impact of this adverse effect, a meta-analysis comparing colistin with other antibiotics in treating MDR-GNB infections was conducted. The PubMed, Embase and Cochrane Library electronic databases were searched up to 31 December 2018 for cohort studies and randomised controlled trials with at least two arms with one arm containing colistin-based treatment. The primary endpoint was the incidence of AKI. The secondary endpoint was 30-day all-cause mortality. A total of 34 studies, including 26 regarding colistin-based therapy versus other antibiotics and 9 regarding colistin monotherapy versus combination therapy, were included. The incidence of CA-AKI was 32.3%. Colistin was associated with an 82% higher incidence of AKI than other antibiotics [odd ratio (OR) = 1.82, 95% confidence interval (CI) 1.13-2.92; P = 0.01]. Most CA-AKI events were mild and reversible without a higher rate of mortality or the requirement for renal replacement therapy (RRT). Only 1.0% of patients required RRT for > 4 weeks. Compared with colistin monotherapy, combination therapy was associated with a significantly lower incidence of AKI (OR = 1.46, 95% CI 1.10-1.94; P = 0.009), particularly in combination with a carbapenem (OR = 1.97, 95% CI 1.30-2.99; P = 0.001). In conclusion, CA-AKI might not be an important limitation of colistin in MDR-GNB therapy.

Clinical relevance of in vitro synergistic activity of antibiotics for multidrug-resistant Gram-negative infections: A systematic review

OBJECTIVES

The aim of this review was to investigate the outcomes of patients infected with multidrug-resistant (MDR) or extensively drug-resistant (XDR) Gram-negative bacteria following synergy-guided antibiotic combination therapy (SGACT).

METHODS

A systematic review of PubMed and Scopus databases was performed. Published studies of any design reporting outcomes of patients with MDR Gram-negative bacteria treated with SGACT were included. Two reviewers independently assessed the relevancy and quality of the retrieved articles and extracted the available data.

RESULTS

Nineteen reports (530 patients) were included. Eleven case reports/series described 26 cases of systemic infection due to MDR Gram-negative bacteria treated with SGACT. Five deaths were reported, two of which were attributed to the infection. Six studies (including one randomised controlled trial) provided comparative data for patients treated with SGACT and those treated with unguided combination therapy (UCT) or active monotherapy. In the pooled analysis of unadjusted data from these studies (504 patients), there was no difference between SGACT and UCT or monotherapy (OR=0.47, 95% CI 0.21-1.04; I²=52%). Analysis of adjusted data showed that SGACT was significantly associated with survival (OR=0.44, 95% CI 0.20-0.98; I²=54%).

CONCLUSION

These limited but promising findings warrant further investigation of SGACT in the outcome of patients with MDR Gram-negative infections in well-designed trials.

Safety and efficacy of colistin alone or in combination in adults with Acinetobacter baumannii infection: A systematic review and meta-analysis

This review comprehensively assessed the safety and efficacy of colistin alone or in combination in adults with Acinetobacter baumannii infection. PubMed, Embase and the Cochrane Library were searched from inception to March 2018 for studies evaluating colistin monotherapy compared with other antibiotic therapy or colistin-based combination therapy for the treatment of A. baumannii infection in adults. Efficacy outcomes were clinical response and microbiological cure. Safety outcomes were mortality and nephrotoxic adverse events. A total of 4 randomised controlled trials (RCTs) and 14 observational studies were identified, including 7 reporting colistin versus other antibiotics and 12 reporting colistin monotherapy versus colistin-based combination therapy. Overall clinical response, microbiological response and mortality did not differ significantly between colistin monotherapy versus other antibiotics. However, the incidence of nephrotoxicity was significantly higher in colistin monotherapy (OR = 2.50, 95% CI 1.05-5.98; P = 0.04). No significant differences were detected in clinical response and >28-day mortality between colistin monotherapy and combination therapy. However, colistin-based combination therapy showed an increased microbiological response (OR = 0.49, 95% CI 0.32-0.74; P = 0.0009) and decreased incidence of nephrotoxicity (OR = 1.66, 95% CI 0.99-2.78; P =0.05). In conclusion, colistin alone is as effective as other antibiotics for the treatment of A. baumannii infection but has a higher risk of nephrotoxicity. Colistin-based combination therapy demonstrated a microbiological benefit and no higher risk of nephrotoxicity compared with monotherapy. High-quality RCTs are still needed to confirm the beneficial role of colistin-based combination therapy.

Comparative efficacy and safety of treatment options for MDR and XDR Acinetobacter baumannii infections: a systematic review and network meta-analysis

Objectives

To comprehensively compare and rank the efficacy and safety of available treatment options for patients with MDR and XDR Acinetobacter baumannii (AB) infection.

Methods

We searched PubMed, Embase and the Cochrane register of trials systematically for studies that examined treatment options for patients with MDR- and XDR-AB infections until April 2016. Network meta-analysis (NMA) was performed to estimate the risk ratio (RR) and 95% CI from both direct and indirect evidence. Primary outcomes were clinical cure and microbiological cure. Secondary outcomes were all-cause mortality and nephrotoxic and non-nephrotoxic adverse events.

Results

A total of 29 studies with 2529 patients (median age 60 years; 65% male; median APACHE II score 19.0) were included. Although there were no statistically significant differences between treatment options, triple therapy with colistin, sulbactam and tigecycline had the highest clinical cure rate. Colistin in combination with sulbactam was associated with a significantly higher microbiological cure rate compared with colistin in combination with tigecycline (RR 1.23; 95% CI 1.03-1.47) and colistin monotherapy (RR 1.21; 95% CI 1.06-1.38). No significant differences in all-cause mortality were noted between treatment options. Tigecycline-based therapy also appeared less effective for achieving a microbiological cure and is not appropriate for treating bloodstream MDR- and XDR-AB infections.

Conclusions

Combination therapy of colistin with sulbactam demonstrates superiority in terms of microbiological cure with a safety profile similar to that of colistin monotherapy. Thus, our findings support the use of this combination as a treatment for MDR- and XDR-AB infections.

Intravenous polymyxins: Revival with puzzle

With the increasing incidence of multi-drug resistant strains, especially carbapenem resistant strains, polymyxsins (mainly colistin and polymyxin B) based regimens seem to be a revival as an effective treatment of last resort in these infections. Evidence from 47 clinical trials or case series we reviewed showed that polymyxins based regimens are effective and have less toxicity compared with previous trials. When used alone, the mortality of intravenous polymyxsins ranged from 0% to 74.3%, clinical response (cure and improvement) rate was 7-82.1%, and microbiological eradication was 27.3-73.9%. The main reasons for the combination therapy are to get potential synergistic effects and to prevent the selection of heteroresistant strains. Several studies showed combination therapy seemed to be more effective than monotherapy, though a few doubts remain. Clinically, polymyxsins can be used in combination with several antibiotics, such as carberpenem, sulbactam, tigecycline, fosfomycin, glycopeptide, rifampicin and so on, but the optimal combination regimen is yet to be confirmed. The optimal dose of polymyxins is also controversial. With the limited clinical evidence, it's suggested loading dose regimens may be more effective, but more attention should be paid to adverse effects. Although recommended in some studies, high dose polymxins regimens with inconsistent clinical evidence need more trials to confirm. It is important to note that concerning dosing regimens, colistin and polymyxin B are not quite the same. In renal impaired patients polymyxin B should be prescribed without dosing adjustment. Risk of renal failure may increase in the following situations, such as the combination of intravenous colistin plus intravenous vancomycin, higher doses-colistin, and intravenous colistin combined with inhalational colistin. In conclusion, there're still controversies in combination regimens, dosing strategies and so on. Prospective trials of lager sample size are needed.

Intravenous colistin combination antimicrobial treatment vs. monotherapy: a systematic review and meta-analysis

BACKGROUND

To evaluate whether intravenous colistin in combination with other antibiotics (IVCC) is associated with lower mortality compared with intravenous colistin monotherapy (IVCM), and to identify factors influencing study outcomes.

METHODS

PubMed and Scopus were searched up to November 2016. Studies were included if they evaluated adult patients with multi-drug-resistant (MDR) or extensively-drug-resistant Gram-negative infections, and reported comparative mortality data (adjusted and unadjusted) for patients receiving IVCC vs. IVCM. Random effects meta-analyses were performed.

FINDINGS

Thirty-two studies (29 observational, three randomized) were included. The overall quality of data was low to very low, and studies were characterized by the lack of adjusted data. The majority of studies were not designed to evaluate the outcome of the meta-analysis, and focused mainly on infections due to Acinetobacter baumannii and Klebsiella pneumoniae. Colistin was administered at variable doses, with or without a loading dose, and in combination with several antibiotics. Overall, IVCC was not associated with lower mortality than IVCM [32 studies, 2328 patients, risk ratio (RR) 0.91, 95% confidence interval (CI) 0.81-1.02, I2 8%]. A significant difference was observed in favour of IVCC when high-dose (>6 million international units) colistin was used (RR 0.80, 95% CI 0.69-0.93), in studies conducted in Asia (RR 0.82, 95% CI 0.71-0.95), in patients with bacteraemia (RR 0.75, 95% CI 0.57-0.98) and in patients with acinetobacter infections (RR 0.88, 95% CI 0.78-1.00).

INTERPRETATION

Overall, low-quality data suggest that IVCC did not lower mortality in patients with MDR Gram-negative infections. However, there is some evidence for a benefit observed with high intravenous doses of colistin.

Meta-analysis of colistin for the treatment of Acinetobacter baumannii infection

Multidrug resistant among Acinetobacter baumannii infection is associated with a high mortality rate and limits the therapeutic options. The aim of this study was to assess the safety and efficacy of colistin monotherapy vs. other single antibiotic therapy AND colistin-based combination therapy (with other antibiotics) vs. colistin alone for the treatment of Acinetobacter baumannii infection. Online electronic database were searched for studies evaluating colistin with or without other antibiotics in treatment of patients with drug-resistant Acinetobacter baumannii infection. Totally, twelve studies met the inclusion criteria. For colistin-based combination therapy, six articles including 668 patients were included. Our results showed that the overall clinical response did not differ significantly between colistin-based combination therapy and monotherapy (OR = 1.37, 95% CI = 0.86-2.19, P = 0.18). This insignificance was also detected in ICU mortality, length of stay and nephrotoxicity (P > 0.05). However, the colistin-based combination therapy was shown increasing the microbiological response (OR = 2.14, 95% CI = 1.48-3.07, P < 0.0001). For colistin monotherapy, six studies involving 491 patients were analyzed. The results were in concordance with the findings of the colistin-based combination therapy group. Our results suggest that colistin may be a promising therapy as safe and efficacious as standard antibiotics for the treatment of drug-resistant Acinetobacter baumannii infection.

Colistin for lung infection: an update

Increasing incidence of resistance of gram-negative bacteria against even newer antibiotic including carbapenem has generated interest in the old antibiotic colistin, which are being used as salvage therapy in the treatment of multidrug resistant infection. Colistin has excellent bactericidal activity against most gram-negative bacilli. It has shown persist level in the liver, kidney, heart, and muscle; while it is poorly distributed to the bones, cerebrospinal fluid, lung parenchyma, and pleural cavity. Being an old drug, colistin was never gone through the drug development process needed for compliance with competent regulatory authorities that resulted in very much limited understanding of pharmacokinetic (PK) and pharmacodynamic (PD) parameters, such as C_max/MIC ratio, AUC/MIC and T > MIC that could predict the efficacy of colistin. In available PK/PD studies of colistin, mean maximum serum concentration (C_max) of colistin were found just above the MIC breakpoint at steady states that would most probably lead to suboptimal for killing the bacteria, even at dosages of 3.0 million international units (MIU) i.e., 240 mg of colistimethate sodium (CMS) intravenously every 8 h. These finding stresses to use high loading as well as high maintenance dose of intravenous colistin. It is not only suboptimal plasma concentration of colistin but also poor lung tissue concentration, which has been demonstrated in recent studies, poses major concern in using intravenous colistin. Combination therapy mainly with carbapenems shows synergistic effect. In recent studies, inhaled colistin has been found promising in treatment of lung infection due to MDR gram-negative bacteria. New evidence shows less toxicity than previously reported.

Colistin for the treatment of ventilator-associated pneumonia caused by multidrug-resistant Gram-negative bacteria: a systematic review and meta-analysis

Ventilator-associated pneumonia (VAP) caused by multidrug-resistant (MDR) Gram-negative bacteria (GNB) has emerged as an important and intractable clinical problem. This review assessed the efficacy and safety of colistin for treatment of MDR GNB VAP. PubMed and Embase were searched for controlled studies of colistin for treatment of MDR GNB VAP. The Mantel-Haenszel random-effects model was used to pool odds ratios (ORs) with 95% confidence intervals (CIs). The primary outcome was clinical cure; secondary outcomes were microbiological eradication, ICU mortality, hospital mortality, length of ICU stay and nephrotoxicity. Fourteen controlled studies involving 1167 patients were identified, including six reporting colistin versus β-lactam antibiotics, three reporting aerosolised (AS) plus intravenous (IV) colistin versus IV colistin alone and five reporting colistin combined therapy versus colistin monotherapy. The clinical cure rate of colistin was comparable with that of β-lactam antibiotics (OR=1.00, 95% CI 0.68-1.47). Compared with IV colistin alone, AS plus IV colistin exhibited a better clinical cure (OR=2.12, 95% CI 1.40-3.20). Compared with colistin monotherapy, colistin combined therapy did not appear to provide a better clinical cure (OR=1.38, 95% CI 0.81-2.33). There was no significant difference in nephrotoxicity and other secondary outcomes between the treatment groups. Colistin appears as effective and safe as β-lactam antibiotics for the treatment of MDR GNB VAP. AS colistin may be a beneficial adjunct to IV colistin in the management of MDR GNB VAP. Colistin combined therapy does not appear to provide better outcomes compared with colistin monotherapy.

Efficacy and safety of polymyxins for the treatment of Acinectobacter baumannii infection: a systematic review and meta-analysis

BACKGROUND

Multi-drug resistance among Acinetobacter baumannii increases the need for polymyxins. We conducted a meta-analysis aimed to assess the efficacy and safety of polymyxins for the treatment of Acinetobacter baumannii infection.

METHODS

We searched PUBMED, EMBASE, the Cochrane Central Register of Controlled Trials (CENTRAL), CNKI, Chinese Biomedical Literature Database up to November 1, 2013, to identify published studies, and we searched clinical trial registries to identify completed unpublished studies. Randomized controlled trials and cohort studies were considered for inclusion. Data were extracted on clinical response, microbiological response, mortality, length of stay and adverse events.

RESULTS

12 controlled studies, comparing 677 patients, were included. Although clinical (odds ratio 1.421, 95% confidence interval 0.722-2.797) and microbiological (OR 1.416, 95% CI 0.369-5.425) response rates favored the polymyxins group, these differences were not significant. Treatment with polymyxins vs. controls did not affect hospital mortality (OR 0.506, 95% CI 0.101-2.536), lengths of hospital stay (standard mean difference -0.221, 95% CI 0.899-0.458) or nephrotoxicity (OR 1.192, 95% CI 0.436-3.261). The combination of polymyxins with other antibiotics achieved similar clinical response rates to its monotherapy regimen (OR 0.601, 95% CI 0.320-1.130).

CONCLUSIONS

Our results suggest that polymyxins may be as safe and as efficacious as standard antibiotics for the treatment of A. baumannii infection. There is no strong evidence that combination regimen of polymyxins is superior to monotherapy regimen.