What is the empirical antibiotic of choice for suspected gram-positive bacilli bacteremia from a urinary source?

From the Guidelines

For suspected gram-positive bacilli bacteremia from a urinary source, high-dose ampicillin (18-30 g IV daily in divided doses) or amoxicillin 500 mg IV or PO every 8 h daily is recommended as the empirical antibiotic of choice, as it provides good coverage against most gram-positive organisms, including vancomycin-resistant enterococci (VRE) 1.

Key Considerations

• The choice of antibiotic should be based on the severity of the infection, the patient's renal function, and the potential for resistance.
• High-dose ampicillin or amoxicillin is recommended due to its bactericidal activity and ability to achieve high urinary concentrations, which can help overcome resistance.
• The duration of therapy typically ranges from 7-14 days, depending on the clinical response and source control, with longer courses sometimes needed for complicated infections.

Alternative Options

• Linezolid 600 mg IV or PO every 12 h may be considered as an alternative option, particularly for patients with severe infections or those who are intolerant to ampicillin or amoxicillin 1.
• Daptomycin 8-12 mg/kg IV daily may also be considered, especially for patients with VRE bacteremia, although its use should be guided by susceptibility testing and clinical response 1.

Important Notes

• It is essential to differentiate colonization from true infection prior to empiric prescription of anti-VRE antimicrobial agents.
• Combination antimicrobial therapy may be considered in severely ill patients or those who fail treatment with traditional options.
• Tigecycline, fosfomycin, and nitrofurantoin may be considered for uncomplicated urinary tract infections due to VRE, but their use should be guided by susceptibility testing and clinical response 1.

From the Research

Empirical Antibiotic Choice for Suspected Gram-Positive Bacilli Bacteremia from a Urinary Source

• The choice of empirical antibiotic for suspected gram-positive bacilli bacteremia from a urinary source depends on various factors, including the suspected pathogen and its resistance pattern 2.
• For enterococcal urinary tract infections (UTIs), ampicillin is generally considered the drug of choice for ampicillin-susceptible enterococcal UTIs, including vancomycin-resistant enterococci (VRE) 2.
• Nitrofurantoin, fosfomycin, and doxycycline have intrinsic activity against enterococci, including VRE, and are possible oral options for VRE cystitis 2.
• Linezolid and daptomycin should be reserved for confirmed or suspected upper and/or bacteremic VRE UTIs among ampicillin-resistant strains 2.
• Vancomycin remains a first-line treatment drug for methicillin-resistant Staphylococcus aureus (MRSA) bacteremia 3.
• The empirical combination of vancomycin and a β-lactam (either nafcillin, oxacillin, or cefazolin) for staphylococcal bacteremia may improve infection-related clinical outcomes 4.

Considerations for Specific Antibiotics

• Daptomycin has bactericidal activity against VRE, but its use is not approved for the treatment of VRE bacteremia 5.
• Linezolid has bacteriostatic activity and is approved for the treatment of VRE infections, but its use may be associated with a lower mortality than daptomycin treatment for VRE bacteremia 5.
• Vancomycin serum concentrations should be monitored to ensure effective treatment and minimize the risk of nephrotoxicity 6.