Development of a combination antibiogram for Pseudomonas aeruginosa bacteremia in an oncology population

Purpose

Development of a combination antibiogram to identify combinations of antibiotics that have the highest likelihood of attaining one active agent in the empiric management of presumed Pseudomonas aeruginosa bacteremia.

Methods

Patients with cancer and P. aeruginosa bacteremia from January 1 to December 31, 2012 were included in this analysis. The primary outcome was identification of effective combinations of beta-lactam and non-betalactam agents. An effective combination was defined as one which achieved in-vitro activity to greater than or equal to 85% of isolates collected. Furthermore, the addition of the non-beta-lactam agent was required to increase the in-vitro activity by at least 5% over beta-lactam monotherapy. Multiple secondary outcomes were evaluated.

Results

One hundred and twenty-three P. aeruginosa isolates were included from 99 patients. Single agent beta-lactam sensitivities ranged from 72.4 to 79.7%. Combination regimen sensitivities ranged from 73.5 to 96.7%. All combination regimens that included a beta-lactam plus an aminoglycoside were found to be effective per the study definition. Independent risk factors for MDR P. aeruginosa were receipt of intravenous (IV) antibiotics within 90 days and hospital length of stay (LOS) greater than or equal to five days. Increasing the number of antibiotics received was associated with a decrease in survival to hospital discharge.

Conclusions

Effective combination regimens included all beta-lactam aminoglycoside regimens. Receipt of IV antibiotics within 90 days and hospital LOS greater than or equal to five days were independent risk factors for MDR isolates.

Extensively drug-resistant Acinetobacter baumannii in a Thai hospital: a molecular epidemiologic analysis and identification of bactericidal Polymyxin B-based combinations

Background

Limited knowledge of the local molecular epidemiology and the paucity of new effective antibiotics has resulted in an immense challenge in the control and treatment of extensively drug-resistant (XDR) Acinetobacter baumannii infections in Thailand. Antimicrobial combination regimens may be the only feasible treatment option in such cases. We sought to characterize the local molecular epidemiology and assess the bactericidal activity of various antibiotics individually and in combination against XDR A. baumannii in a Thai hospital.

Methods

All XDR A. baumannii isolates from Thammasat University Hospital were collected between October 2010 and May 2011. Susceptibility testing was conducted according to reference broth dilution methods. Pulse-field gel electrophoresis was used to genotype the isolates. Carbapenemase genes were detected using polymerase chain reaction. In vitro testing of clinically-relevant concentrations of imipenem, meropenem, doripenem, rifampicin and tigecycline alone and in combination with polymyxin B was conducted using multiple combination bactericidal testing.

Results

Forty-nine polymyxin B-susceptible XDR A. baumannii isolates were identified. bla_OXA-23 and bla_OXA-51 genes were detected in all isolates. Eight clonally related clusters were identified, resulting in the initiation of several infection control measures. Imipenem, meropenem, doripenem, rifampicin, and tigecycline in combination with PB respectively, exhibited bactericidal killing in 100%, 100%, 98.0%, 100% and 87.8% isolates respectively at 24 hours.

Conclusion

Molecular epidemiologic analysis can aid the early detection of infection outbreak within the institution, resulting in the rapid containment of the outbreak. Imipenem/meropenem/rifampicin in combination with polymyxin B demonstrated consistent bactericidal effect against 49 bla_OXA-23-harbouring XDR A. baumannii clinical isolates, suggesting a role of combination therapy in the treatment of these infections.

Role of Unit-Specific Combination Antibiograms for Improving the Selection of Appropriate Empiric Therapy for Gram-Negative Pneumonia

In an effort to improve the selection of appropriate empiric gram-negative therapy for pneumonia, we examined intensive care unit-specific combination antibiograms. These antibiograms were able to predict appropriate empiric gram-negative therapy. Empiric combination therapy based on unit-specific combination antibiograms may aid in the selection of therapy for gram-negative pneumonia.

Carbapenem de-escalation therapy in a resource-limited setting

Pulmonary infection (P=.01) and an infectious diseases consultation (P=.04) were associated with carbapenem de-escalation; pulmonary infection and septic shock were associated with unsuccessful de-escalation. Successful de-escalation was associated with lower mortality (0% vs 23%; P<.001) and shorter duration of carbapenem use (4 vs 10 days; P ≤ .001).

Managing antimicrobial resistance in intensive care units

The challenges in managing patients with infection in the intensive care unit are increased in an era where there are dwindling antimicrobial choices for multidrug-resistant pathogens. Clinicians in the intensive care unit must balance between choosing appropriate antimicrobial treatment for patients with suspected infection and utilizing antimicrobials in a judicious fashion. Improving antimicrobial utilization is a critical component to reducing antimicrobial resistance. Although providing effective antimicrobial therapy and improving antimicrobial utilization may seem to be competing goals, there are effective strategies to accomplish both. Antimicrobial stewardship programs provide an organized way to implement these strategies and can enhance the intensive care unit physician's success in improving patient outcomes and combating antimicrobial resistance in the intensive care unit.

Optimizing empirical antimicrobial therapy for infection due to gram-negative pathogens in the intensive care unit: utility of a combination antibiogram

OBJECTIVE

To determine whether the use of dual antimicrobial therapy based on the results of a combination antibiotic susceptibility report (antibiogram) increases the likelihood of selecting adequate empirical coverage in critically ill patients with infection due to potentially resistant gram-negative pathogens.

DESIGN

Retrospective data analysis.

SETTING

Urban academic medical center.

METHODS

An analysis of culture results and susceptibility data from intensive care unit patients determined by the clinical microbiology laboratory was performed. The proportion of 5 common gram-negative pathogens susceptible to monotherapy with 1 of 3 antipseudomonal antibiotics (piperacillin-tazobactam, ceftazidime, or imipenem) was compared with the proportion susceptible to each of these 3 "backbone" agents plus 1 of 4 additional antimicrobial agents used in combination.

RESULTS

More than 5,000 clinical isolates were examined. When all isolates recovered during the entire study period were included, the addition of any of the second antibiotics studied to each of the 3 backbone agents significantly increased the likelihood of covering the causative pathogen (P < .01 for each). The benefit of combination therapy was variable when results for each of the 5 organisms were examined individually. When temporal trends in susceptibility were examined, the decrease in the proportion of organisms susceptible to monotherapy was statistically significant for both imipenem and ceftazidime (P < .01).

CONCLUSIONS

Reporting antibiotic susceptibility data in the form of a combination antibiogram may be useful to clinicians who are considering empirical antimicrobial therapy in the intensive care unit.