Bacteremia Clinical Trial
Official title:
Multi-center, Open-label Randomized Controlled Trial on the Efficacy of Combination Antibiotic Therapy for Serious Infections Caused by Extensively Drug-resistant Gram-negative Bacteria (XDR-GNB)
Background and rationale:
Antimicrobial resistance is a global public health threat. An increasing number of
Gram-negative bacteria isolates worldwide are resistant to virtually all antibiotics
including carbapenems. Although polymyxins are the current gold standard antibiotic for
treatment of severe extensively drug-resistant Gram-negative bacteria (XDR-GNB - defined in
Appendix I) infections, resistance development on therapy and treatment failures are common.
Combination antibiotics therapy have better in vitro efficacy, but have not been formally
tested in a prospective trial.
We will conduct a Phase IIB, prospective, open-label, randomized-controlled trial in 4 major
Singaporean hospitals, with balanced treatment assignments achieved by permuted block
randomization, stratified by hospital. There will be 75 subjects per arm, with the subjects
in the comparator arm receiving standard-dose polymyxin B while the intervention arm will
receive a second antibiotic, doripenem, with polymyxin B against the bacterial isolate in
question. Subjects with ventilator-associated pneumonia (VAP) will additionally receive
nebulized colistin. The primary outcome is 30-day mortality while secondary outcomes include
microbiological clearance, time to defervescence, and toxicity of therapy, presence of
secondary infections due to new multi-drug resistant bacteria and length of ICU stay. Plasma
drug levels will be measured by liquid chromatography-mass spectrometry.
Hypothesis:
The underlying primary hypothesis is that combination antibiotic therapy (IV polymyxin B + IV
doripenem) is superior to mono-antibiotics therapy (IV polymyxin B) in reducing 30-day
mortality from XDR-GNB infections.
Antimicrobial resistance is a global public health threat and the theme of the World Health
Day 2011. While the issue in most cases (such as extensively-drug-resistant tuberculosis,
antiviral-resistant human immunodeficiency virus and drug-resistant malaria) is the access to
effective antimicrobial agents and/or the high cost of these drugs, for a small but
increasing number of nosocomial drug-resistant Gram-negative bacteria, there is no safe and
effective antibiotic available - not now nor in the next 10-year horizon, given the timeline
of drug development. Extensively-drug-resistant Gram-negative bacilli (XDR-GNB) include the
majority of the six organisms on the Infectious Disease Society of America's (IDSA's) watch
list of global "bad bugs" for which the development of new drugs was urgently required. These
Gram-negative bacilli are Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa,
and Acinetobacter baumannii. The most frequently isolated of these organisms in the Singapore
hospital setting is XDR-A. baumannii at this point in time.
A. baumannii has swiftly emerged over the past three decades as a major nosocomial
opportunistic pathogen, causing infections in debilitated patients especially in the
intensive care unit (ICU) setting. It is the 10th most frequently isolated pathogen in US
hospitals but ranks among the top 5 pathogens in tropical hospitals including Singapore,
where the number of antibiotic-resistant A. baumannii infections exceeded 700 cases in 2006.
The major issue with A. baumannii is that the organism has rapidly developed resistance to
many antibiotics - as an example, within a single decade (1995 to 2004) in US hospitals,
carbapenem resistance in A. baumannii increased from 9% to 40%. XDR-A. baumannii (defined as
A. baumannii resistant to all antibiotics - including carbapenems,
beta-lactam/beta-lactamase-inhibitors, cephalosporins, aminoglycosides, fluoroquinolones,
tetracyclines and sulphonamides - with the exception of the polymyxins and tigecycline) has
now been described causing infections in hospitals worldwide. Mortality associated with
severe infections caused by multidrug-resistant A. baumannii and other XDR-GNB has ranged
between 30% and 70% depending on the clinical setting and condition of the patients. Locally,
the mortality from severe XDR-GNB infections is approximately 40%. From 2006 to 2010, there
was an average of 140 cases of severe XDR-GNB infections in local hospitals each year,
translating to approximately 56 deaths from infections attributable to this organism alone in
Singapore every year. Other local XDR-GNB includes XDR-P. aeruginosa, and
carbapenemase-producing E. coli and K. pneumoniae (carriage of New Delhi
metallo-beta-lactmase-1 (NDM-1), OXA-48 and Klebsiella pneumoniae carbapnemase (KPC) genes).
These remain relatively rare in Singapore, with fewer than 30 severe infections in local
hospitals each year.
Treatment of infections caused by XDR-GNB presents a considerable challenge for clinicians.
Monotherapy polymyxins - commercially available as polymyxin B or polymyxin E (colistin) -
are currently the gold standard of treatment for severe XDR-GNB infections. However, they are
associated with significantly more adverse effects and may be less effective clinically
compared to other antibiotics, such as the beta-lactams. In one tertiary center in Korea,
retrospective analysis suggested that mortality of XDR-A. baumannii bacteremia was not
reduced when colistin was used for treatment compared to other antibiotics (to which the
organisms were resistant). Individual treatment failures with polymyxins have been reported,
either due to the development of resistance in vivo or inherent heterogeneous polymyxin
resistance - a phenomenon where many isolates that appear susceptible to the drug may
actually harbor polymyxin-resistant subpopulations. Tigecycline susceptibility in XDR-GNB is
variable and clinical failures have also been reported, particularly for bloodstream
infections due to the low achievable concentrations of the drug in serum as well as the
potential for development of resistance during treatment. This has led to some experts
advocating combination antibiotic therapy as an alternative.
In general, combination antibiotics have performed better than single agent polymyxin B in in
vitro time-kill studies and animal models of infection. In accordance with other published
reports, we have also shown that various antibiotic combinations demonstrated synergistic
activity against XDR-GNB. The most effective in vitro combinations for local XDR-GNB isolates
have been polymyxin B + rifampicin and polymyxin B + doripenem, with additive/synergistic
effect in up to 50% of isolates without antagonism seen in the other isolates. However, it is
uncertain if in vitro results in this particular instance directly predict clinical outcomes.
No rigorous clinical trials have been completed to date and existing results based on case
series and retrospective reviews are conflicting. Against local XDR-P. aeruginosa, however,
dual antibiotic therapy appears to be less promising, with synergism achieved only when
triple antibiotic combinations were tested.
Other in vitro studies have suggested that triple antibiotic combinations may be more
effective than dual antibiotic combinations. Nonetheless, this is difficult to recommend in
clinical practice at the current time because of the very probable rise in adverse effects
versus uncertain benefits.
Because of the increasing number of XDR-GNB infections locally and worldwide, the
questionable efficacy of the current gold standard monotherapy treatment, the paucity of
novel and effective antibiotics against such infections for the foreseeable 10-year horizon,
and the consistent reports of superiority in in vitro studies, it is critically important
that combination therapy should be tested against polymyxin monotherapy in a rigorous
clinical trial to ascertain if it represents a more effective treatment strategy. It is also
important to determine if the results of multiple combinations bactericidal testing - like
more standardized susceptibility testing for single antibiotics - will correlate well with
clinical outcomes.
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