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Nathan Jones, Punit J Shah, Challenges in antimicrobial susceptibility testing interpretation: Fluoroquinolone susceptibility discordance, American Journal of Health-System Pharmacy, Volume 79, Issue 11, 1 June 2022, Pages 829–830, https://doi.org/10.1093/ajhp/zxac039
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The continued widespread development of antimicrobial resistance has led to a trend of continuously rising reported minimum inhibitory concentrations (MICs) for many antibiotics. In vitro pharmacokinetic-pharmacodynamic studies and clinical data may provide information to establish antimicrobial susceptibility breakpoints. This information needs to be continually monitored and reviewed, with susceptibility breakpoints updated to provide patients with optimal anti-infective medication regimens. However, susceptibility breakpoints can be discordant among the multiple organizations that publish them, including the Clinical and Laboratory Standards Institute (CLSI), the Food and Drug Administration (FDA), the European Committee on Antimicrobial Susceptibility Testing, and the US Committee on Antimicrobial Susceptibility Testing.
If susceptibility interpretations are not updated in real time based on current literature, patients could be inadvertently treated with an ineffective agent when intermediate or resistant MICs are interpreted and reported as susceptible. This is further complicated because interpretation of antibiotic susceptibilities is not always immediately updated, especially if the update requires FDA approval. Many hospitals and other organizations utilize automated machines to determine susceptibility (for example, BD Phoenix and bioMérieux Vitek instruments). Each machine’s manufacturer may have to submit a new drug application through FDA to have reportable MIC breakpoints updated. Providing optimized antimicrobial therapy during this time interval becomes challenging as reported susceptibility may not be in line with current published MIC cut points. In some cases, an institution may complete internal validation to customize susceptibility interpretation, but this is not always feasible or allowable because FDA clearance may be required for any updates or revisions to breakpoints. Throughout the often lengthy time period required to update standards, old and inaccurate interpretations are presented to frontline staff.
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