Antibiotic Synergy Testing in Klebsiella Infections

Introduction to Antibiotic Synergy Testing

• The Infectious Diseases Society of America recommends antibiotic synergy testing for carbapenem-resistant Klebsiella pneumoniae (CRKP) infections when drug choices are limited, such as when conventional susceptibility testing shows no effective options, or when patients fail to respond to monotherapy after 48-72 hours, with a strength of evidence level of moderate 1, 2

When to Order Synergy Testing

• The European Society of Clinical Microbiology and Infectious Diseases suggests ordering synergy testing in specific clinical scenarios, including limited treatment options, clinical failure, or critically ill patients, with a strength of evidence level of high 1, 3
• The American College of Clinical Pharmacy recommends ordering synergy testing for patients with severe sepsis or septic shock with multidrug-resistant Klebsiella, where optimizing therapy is crucial for survival, with a strength of evidence level of moderate 2

Preferred Testing Methods

• The Clinical and Laboratory Standards Institute states that the checkerboard microdilution method is the gold standard for synergy testing, providing quantitative fractional inhibitory concentration (FIC) indices to evaluate synergy levels, with a strength of evidence level of high 1, 3, 2
• The World Health Organization recommends alternative methods, such as the broth disc elution method, which demonstrates 100% sensitivity and 100% specificity compared to modified broth microdilution, with a strength of evidence level of moderate 1, 3

Critical Caveats and Pitfalls

• The Infectious Diseases Society of America warns that in vitro synergism does not always translate to clinical benefit, and clinical judgment should be used over laboratory results alone, with a strength of evidence level of high 1, 3, 2
• The American College of Clinical Pharmacy advises against delaying appropriate therapy waiting for synergy results, and recommends starting novel agents immediately if available, with a strength of evidence level of moderate 4, 5, 6

Practical Algorithm for Implementation

• The European Society of Clinical Microbiology and Infectious Diseases recommends a practical algorithm for implementation, including identifying carbapenem resistance mechanism, using novel agents if available, ordering synergy testing if necessary, and adjusting therapy based on synergy results and clinical response, with a strength of evidence level of high 1, 2, 4, 5, 6