Do you recommend the use of ampicillin/ceftriaxone for prosthetic valve endocarditis due to ampicillin-susceptible Enterococcus faecium?

The prognosis for Enterococcus faecalis endocarditis is generally better than that for Enterococcus faecium, primarily due to antibiotic susceptibility patterns. It is fortunate to have an ampicillin-susceptible strain of E. faecium in this case of prosthetic valve infective endocarditis. In general, I prefer using a double beta-lactam antibiotic therapy over a combination therapy that includes gentamicin, regardless of the enterococcal species involved, provided the strains are susceptible. This is due to less risk for adverse events with comparable effectiveness. Most of the patients are 65-75 years of age and remain at high risk for nephrotoxicity, and that reason alone might justify its use.

Since even ampicillin-susceptible Enterococci lack robust autolytic enzymes, ampicillin is actually bacteriostatic against this organism even with prolonged incubation. For this reason, I like a 4-6 week combination treatment with amp+CTR, which is bactericidal since these antibiotics target different penicillin-binding proteins.

Agree with ampicillin/penicillin + ceftriaxone for most patients (there are often complexities to this decision). There was decent evidence for this, even a decade ago, referenced in the IDSA/AHA infective endocarditis guidelines (Baddour et al., PMID 26373316), where AMP + CRO is a class IIa, level B recommendation. The guidelines do not even consider ampicillin/penicillin monotherapy as a frontline option. There is more recent evidence that the ceftriaxone MIC of the organism may play a role in determining synergistic effects, but ceftriaxone AST isn't typically performed on enterococcal isolates, and the harm in adding ceftriaxone is comparatively low for most patients. I would be concerned about using ampicillin/penicillin monotherapy a...

I do not recommend adding ceftriaxone as a second agent for Enterococcus endocarditis, as this approach is not supported by evidence-based medicine. No large randomized trials have demonstrated that dual therapy is superior to ampicillin monotherapy.

I would use dual therapy. Prior to Dr. Moellering's seminal work in this area describing synergy between penicillin and streptomycin, the cure rate for enterococcus endocarditis clinically was in the 40% range. This nearly doubled with the use of synergistic treatment using penicillin and streptomycin.