What medication would you recommend in addition to Augmentin (amoxicillin/clavulanate) to treat a urinary tract infection with Proteus mirabilis and Enterococcus faecalis?

Treatment of UTI with Proteus mirabilis and Enterococcus faecalis

For a urinary tract infection with both Proteus mirabilis and Enterococcus faecalis, gentamicin should be added to Augmentin (amoxicillin/clavulanate) for optimal treatment, as it provides synergistic coverage against Enterococcus while Augmentin effectively treats the Proteus infection.

Rationale for Combination Therapy

• Augmentin (amoxicillin/clavulanate) alone is effective against Proteus mirabilis but may benefit from additional coverage for Enterococcus faecalis in complicated or polymicrobial infections 1, 2
• Gentamicin provides synergistic activity against Enterococcus faecalis when combined with beta-lactams like amoxicillin (contained in Augmentin) 1
• This combination therapy approach is supported by guidelines for treating infections with these specific organisms, particularly when both are present simultaneously 1

Antimicrobial Selection Considerations

For Proteus mirabilis:

• Proteus mirabilis in this case is susceptible to Augmentin, which is already part of the treatment plan 2, 3
• Augmentin effectively treats amoxicillin-resistant strains of Proteus due to the beta-lactamase inhibitor (clavulanic acid) component 4
• Recent evidence supports Augmentin's effectiveness against resistant Enterobacterales in urinary tract infections 5

For Enterococcus faecalis:

• Enterococcus faecalis is susceptible to ampicillin (similar to amoxicillin in Augmentin) but benefits from synergistic therapy 1
• Guidelines recommend the addition of an aminoglycoside (like gentamicin) to a beta-lactam for enhanced bactericidal activity against Enterococcus 1
• Gentamicin at 3 mg/kg/day IV or IM in a single daily dose provides optimal synergy with the beta-lactam component of Augmentin 1

Dosing Recommendations

• Augmentin: Continue at standard dosing (typically 875 mg PO twice daily) 1, 2
• Add gentamicin: 3-5 mg/kg/day IV or IM as a single daily dose 1
• Duration of therapy: 5-7 days for uncomplicated UTI; 10-14 days for complicated UTI 1

Important Clinical Considerations

• Monitor renal function and gentamicin levels, particularly with extended therapy 1
• Consider local resistance patterns when finalizing therapy choices 1
• If gentamicin cannot be used due to contraindications, alternative options include:
  • Fluoroquinolones (if susceptible): Levofloxacin 500 mg daily or ciprofloxacin 500 mg twice daily 6, 7
  • For Enterococcus with high-level aminoglycoside resistance, consider alternative regimens such as ampicillin plus ceftriaxone 1

Common Pitfalls to Avoid

• Treating only one organism in polymicrobial infections can lead to treatment failure 1
• Underestimating the need for synergistic therapy against Enterococcus faecalis 1
• Failing to monitor for aminoglycoside toxicity with prolonged therapy 1
• Not adjusting therapy based on clinical response and susceptibility results 1

By adding gentamicin to Augmentin, you provide comprehensive coverage for both organisms with synergistic activity against Enterococcus faecalis while maintaining effective treatment for Proteus mirabilis.