Changing antimicrobial prescribing patterns, and laboratory reporting in Enterococcus faecalis infective endocarditis...

Enterococcus faecalis (E. faecalis) infective endocarditis (EFIE) treatment consists of a penicillin backbone and a synergistic agent (gentamicin or ceftriaxone). Due to the instability of aminopenicillins in continuous infusion in the outpatient context, benzylpenicillin is used as an alternative to ampicillin, though concern regarding reduced synergy with ceftriaxone has emerged. Clinical Laboratory Standards Institute (CLSI) provides MIC breakpoints for penicillin and ampicillin. European Committee for Antimicrobial Susceptibility Testing (EUCAST) guidelines only provide breakpoints for ampicillin. We evaluated the changing antimicrobial prescribing practices, and laboratory reporting (from CLSI to EUCAST guidelines) related to EFIE treatment and outcomes at our centre.

This was a retrospective study at Monash Health, Melbourne. Adult patients aged ≥ 18 years, who were treated for EFIE from 2014 to 2022, were included. Univariable associations were evaluated (p < 0.05).

104 patients treated for EFIE were included. Following EUCAST guideline implementation, there was a significant increase in ampicillin-based regimens prescribed as initial antimicrobials for directed EFIE therapy (64.3 to 82.3% p = 0.00135); benzylpenicillin regimens decreased across the same period (36.7% to 8.1%, p = 0.0007). In patients who received combination therapy, ceftriaxone use increased in the EUCAST period (p < 0.0001). Vancomycin prescriptions as subsequent regimen increased in the EUCAST period (0 to 19.3%, p = 0.0071). Ampicillin or benzylpenicillin monotherapy prescription as initial EFIE treatment reduced when comparing CLSI to EUCAST periods (p = 0.00001).

There is significant heterogeneity in the antimicrobials prescribed for EFIE at our centre, reflective of evidence that emerged over the last decade, changes in susceptibility testing and reporting and lack of randomised control trial (RCT) data supporting any one regimen. RCT data is required to further inform and refine directed EFIE treatment recommendations.