What is the treatment for a biliary drain infection with Enterococcus that is resistant to Vancomycin (vancomycin) and Linezolid (linezolid), but susceptible to Gentamicin (gentamicin) and Ampicillin (ampicillin)?

From the Guidelines

For a biliary drain showing Enterococcus resistant to vancomycin and linezolid but susceptible to gentamicin and ampicillin, I recommend treatment with ampicillin as the primary therapy, with consideration of adding gentamicin for a synergistic effect, as supported by the guidelines for infective endocarditis due to Enterococcus spp. 1. The standard dosing for ampicillin would be 2 grams IV every 4-6 hours for adults with normal renal function.

• Key considerations include:
  • Monitoring renal function closely if gentamicin is used due to its nephrotoxicity risk.
  • Ensuring adequate biliary drainage is maintained alongside antibiotic therapy, as source control is essential for successful treatment of biliary infections.
  • The treatment duration should typically be 10-14 days, guided by clinical response and follow-up cultures. This approach is based on the most recent and highest quality evidence available, which emphasizes the importance of using effective antibiotics against the specific strain of Enterococcus, while also considering the potential risks and benefits of different treatment options 1.
• Important points to note:
  • The finding of vancomycin and linezolid resistance is concerning as it limits treatment options and suggests a potentially challenging multidrug-resistant organism.
  • Gentamicin dosing should be 1 mg/kg IV every 8 hours, particularly if the infection is severe or complicated, as per the guidelines 1.
  • The combination of ampicillin and gentamicin is active against Enterococcus faecalis strains with and without high-level aminoglycoside resistance, making it a suitable choice for this scenario 1.

From the FDA Drug Label

The following bacteria are usually resistant to the aminoglycosides, including gentamicin: most streptococcal species (including Streptococcus pneumoniaeand the Group D streptococci), most enterococcal species (including Enterococcus faecalis, E. faecium, and E durans), and anaerobic organisms, such as Bacteroidesspecies and Clostridiumspecies. In vitrostudies show that an aminoglycoside combined with an antibiotic that interferes with cell wall synthesis may act synergistically against some enterococcal strains. The combination of gentamicin and penicillin G has a synergistic bactericidal effect against strains of Enterococcus faecalis, E. faeciumand E. durans An enhanced killing effect against many of these strains has also been shown in vitrowith combinations of gentamicin and ampicillin, carbenicillin, nafcillin or oxacillin.

Gentamicin may be effective against Enterococcus species when used in combination with ampicillin, as it has been shown to have a synergistic bactericidal effect against some enterococcal strains 2. However, gentamicin alone is not effective against most enterococcal species.

• Key points:
  • Gentamicin is not effective against most enterococcal species when used alone.
  • Combination of gentamicin and ampicillin may be effective against some enterococcal strains.
  • The decision to use gentamicin should be based on the results of susceptibility tests and clinical judgment 2.

From the Research

Biliary Drained Shows Enterococcus Resistant to Vancomycin Linezolid and Susceptible to Gentamicin and Ampicillin

• The bacterium is resistant to vancomycin and linezolid, but susceptible to gentamicin and ampicillin, which is a common resistance pattern in enterococci 3.
• The combination of ampicillin and gentamicin has been shown to be effective against Enterococcus faecalis and Enterococcus gallinarum, with synergistic and bactericidal effects 4, 5.
• However, gentamicin can cause nephrotoxicity, which is a concern in patients with pre-existing kidney disease 6.
• An alternative combination is ampicillin and ceftriaxone, which has been shown to be effective against Enterococcus faecalis with no high-level resistance to aminoglycosides, and has lower nephrotoxicity compared to gentamicin 7.
• The choice of antibiotic combination depends on the specific strain of enterococcus, the severity of the infection, and the patient's underlying health conditions.
• It is essential to monitor the patient's kidney function and adjust the antibiotic regimen accordingly to minimize the risk of nephrotoxicity 6, 7.