Outpatient continuous-infusion benzylpenicillin combined with either gentamicin or ceftriaxone for enterococcal endocarditis

Background: Treatment regimens requiring multiple daily dosing for enterococcal endocarditis are challenging to deliver in the outpatient setting. Continuous-infusion benzylpenicillin via a 24 h elastomeric infusor, combined with either once-daily gentamicin or ceftriaxone, requires only one nursing encounter daily and is commonly used in New Zealand. Objectives: To assess the therapeutic success and adverse antibiotic effects of these regimens. Methods: A retrospective observational case series from multiple hospitals of patients aged 15 years or over with enterococcal endocarditis diagnosed between July 2013 and June 2019 who received at least 14 days of outpatient continuous-infusion benzylpenicillin combined with either gentamicin or ceftriaxone for synergy. Results: Forty-three episodes of enterococcal endocarditis in 41 patients met inclusion criteria. The primary synergy antibiotic was gentamicin in 20 episodes and ceftriaxone in 23 episodes. For the 41 initial treatment courses, 31 (76%) patients were cured, 3 (7%) patients developed relapsed endocarditis during or following antibiotic treatment and 7 (17%) patients continued with long-term suppressive oral amoxicillin following IV antibiotic treatment. There was no difference in the relapse rate between the two groups (P=0.59). Seven (35%) adverse antibiotic effects were documented in the gentamicin group and none in the ceftriaxone group (P<0.01). Two deaths (5%) occurred within the 6 month follow-up period. Conclusions: Outpatient treatment of enterococcal endocarditis with continuous-infusion benzylpenicillin combined with either once-daily gentamicin or ceftriaxone following a period of inpatient treatment is usually effective. A significantly higher rate of adverse effects was seen with gentamicin, favouring ceftriaxone as the initial synergy antibiotic.