Impact of Reappraisal of Fluoroquinolone Minimum Inhibitory Concentration Susceptibility Breakpoints in Gram-Negative Bloodstream Isolates

Changing times: The impact of gram-negative breakpoint changes over the previous decade

We assessed breakpoint changes of 13,101 Enterobacterales and Pseudomonas aeruginosa isolates from the past decade. All β-lactams and fluoroquinolones demonstrated decreased susceptibilities following breakpoint changes. Enterobacter cloacae experienced the largest average decrease in susceptibility amongst the Enterobacterales at 5.3% and P. aeruginosa experienced an average decrease in susceptibility of 9.3%.

Evaluating outcomes associated with revised fluoroquinolone breakpoints for Enterobacterales urinary tract infections: A retrospective cohort study

PURPOSE

In 2019, minimum inhibitory concentration (MIC) breakpoints of ciprofloxacin and levofloxacin for Enterobacterales were lowered. This study sought to determine whether there is a correlation between MIC and outcomes in those receiving fluoroquinolones (FQs) for urinary tract infections (UTIs) caused by Enterobacterales pathogens.

METHODS

This was a retrospective study of adult patients treated with ciprofloxacin or levofloxacin for a UTI caused by an Enterobacterales pathogen. Patients were placed into low MIC (ciprofloxacin: ≤ 0.25 mcg/mL; levofloxacin ≤ 0.5 mcg/mL), intermediate MIC (ciprofloxacin: 0.5-2 mcg/mL; levofloxacin: 1-4 mcg/mL), or high MIC groups (ciprofloxacin: > 2 mcg/mL; levofloxacin: > 4 mcg/mL). The primary outcome was UTI recurrence, defined as hospital admission, emergency department or clinic visit due to UTI, or antibiotic prescription within 28 days of FQ initiation.

RESULTS

A total of 1022 patients were included: 887, 75, and 60 with a low, intermediate, and high MIC, respectively. UTI recurrence within 28 days occurred most frequently in the high MIC group (20.5% vs. 25.3% vs. 60%; P < 0.01). Risk factors for UTI recurrence identified by multivariable analysis were those with a high MIC (high vs. low MIC: OR 5.20, 95% CI 2.99-9.05, P < 0.01; high vs. intermediate MIC: OR 4.72, 95%CI 2.22-10.03, P < 0.01), a complicated UTI (OR 1.85, 95% CI 1.35-2.54; P < 0.01), a history of recurrent UTIs (OR 1.84, 95% CI 1.29-2.62; P < 0.01), or a respiratory disorder (OR 1.58, 95% CI 1.04-2.42; P = 0.03).

CONCLUSION

This study supports separate, less stringent FQ MIC breakpoint interpretive criteria for UTIs caused by Enterobacterales pathogens.

Clinical Impact of the Revised 2019 CLSI Levofloxacin Breakpoints in Patients with Enterobacterales Bacteremia

The Clinical and Laboratory Standards Institute (CLSI) revised the fluoroquinolone MIC breakpoints for Enterobacterales in 2019, based on pharmacokinetic/pharmacodynamic analyses. However, clinical evidence supporting these breakpoint revisions is limited. A retrospective study was conducted at 3 hospitals in Taiwan between January 2017 and March 2019. Patients treated with levofloxacin for bacteremia caused by members of the Enterobacterales with high MICs (1 or 2 μg/ml; levofloxacin susceptible by pre-2019 CLSI breakpoints) were compared with those with low-MIC bacteremia (≤0.5 μg/ml; levofloxacin susceptible by 2019 CLSI breakpoints) to assess therapeutic effectiveness by multivariable logistic regression. The primary outcome was 30-day mortality, and the secondary outcome was the emergence of levofloxacin-resistant isolates within 90 days after levofloxacin initiation. A total of 308 patients were eligible for the study. Kaplan-Meier analysis showed that patients infected with high-MIC isolates (n = 63) had a significantly lower survival rate than those infected with low-MIC isolates (n = 245) (P = 0.001). Multivariable logistic regression revealed that high levofloxacin MIC was a predictor of 30-day mortality (odds ratio [OR], 6.05; 95% confidence interval [CI], 1.51 to 24.18; P = 0.011). We consistently found similar results in a propensity score-matched cohort (OR, 5.38; 95% CI, 1.06 to 27.39; P = 0.043). The emergence of levofloxacin-resistant isolates was more common in the high-MIC group than the low-MIC group (25.0% versus 7.5%; P = 0.065). An estimated area under the concentration-time curve/MIC ratio of ≥87 was significantly associated with better survival (P = 0.002). In conclusion, patients infected with isolates with levofloxacin MICs within the pre-2019 CLSI susceptible range of 1 or 2 μg/ml exhibited higher mortality than those infected with isolates with MICs of ≤0.5 μg/ml.

A Critical Evaluation of Newer β-Lactam Antibiotics for Treatment of Pseudomonas aeruginosa Infections

OBJECTIVE

This article critically evaluates common Pseudomonas aeruginosa resistance mechanisms and the properties newer β-lactam antimicrobials possess to evade these mechanisms.

DATA SOURCES

An extensive PubMed, Google Scholar, and ClinicalTrials.gov search was conducted (January 1995 to July 2020) to identify relevant literature on epidemiology, resistance mechanisms, antipseudomonal agents, newer β-lactam agents, and clinical data available pertaining to P aeruginosa.

STUDY SELECTION AND DATA EXTRACTION

Relevant published articles and package inserts were reviewed for inclusion.

DATA SYNTHESIS

Therapeutic options to treat P aeruginosa infections are limited because of its intrinsic and acquired resistance mechanisms. The goal was to identify advances with newer β-lactams and characterize improvements in therapeutic potential for P aeruginosa infections.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

Multidrug-resistant (MDR) P aeruginosa isolates are increasingly encountered from a variety of infections. This review highlights potential activity gains of newer β-lactam antibacterial drugs and the current clinical data to support their use. Pharmacists will be asked to recommend or evaluate the use of these agents and need to be aware of information specific to P aeruginosa, which differs from experience derived from Enterobacterales infections.

CONCLUSIONS

Newer agents, including ceftazidime-avibactam, ceftolozane-tazobactam, imipenem-relebactam, and cefiderocol, are useful for the treatment of MDR P aeruginosa infections. These agents offer improved efficacy and less toxicity compared with aminoglycosides and polymyxins and can be used for pathogens that are resistant to first-line antipseudomonal β-lactams. Selection of one agent over another should consider availability, turnaround of susceptibility testing, and product cost. Efficacy data specific for pseudomonal infections are limited, and there are no direct comparisons between the newer agents.