Recommended Dosage of Amoxicillin and Gentamicin for UTI Caused by Pseudomonas and E. coli
For treating a UTI caused by Pseudomonas and E. coli, the recommended regimen is amoxicillin 3-4 g IV every 6 hours plus gentamicin 15 mg/kg IV once daily. 1
Treatment Rationale
Antimicrobial Selection
The European Association of Urology (EAU) 2024 guidelines strongly recommend using a combination of amoxicillin plus an aminoglycoside for complicated UTIs with systemic symptoms, which is appropriate for mixed infections with both Pseudomonas and E. coli 1. This combination provides:
Broad coverage:
- Amoxicillin targets E. coli
- Gentamicin covers both Pseudomonas and E. coli, including some resistant strains
Synergistic effect: The combination provides enhanced bactericidal activity against both pathogens
Dosing Specifics
Gentamicin
- Dosage: 15 mg/kg IV once daily 1
- Administration: Intravenous
- Duration: 7-14 days (7 days if patient becomes hemodynamically stable and afebrile for at least 48 hours; 14 days for men when prostatitis cannot be excluded) 1
Amoxicillin
- Dosage: 3-4 g IV every 6 hours 1
- Administration: Intravenous
- Duration: Same as gentamicin (7-14 days)
Important Considerations
Monitoring Requirements
- Gentamicin:
- Monitor serum levels to prevent toxicity
- Check renal function before and during treatment
- Monitor for ototoxicity and nephrotoxicity
Urinary Factors Affecting Treatment
- Acidic and concentrated urine can inhibit gentamicin activity, potentially requiring higher doses 2
- Up to 40 times more gentamicin may be needed in concentrated acidic urine compared to standard media 2
Treatment Duration
- 7 days if patient becomes hemodynamically stable and afebrile for at least 48 hours 1
- Extended to 14 days for men when prostatitis cannot be excluded 1
- Duration should be related to treatment of any underlying urological abnormality 1
Alternative Regimens
If the patient cannot tolerate the recommended regimen:
- For Pseudomonas coverage: Consider ceftazidime 2g IV every 8 hours or cefepime 2g IV every 8-12 hours 1
- For multi-drug resistant organisms: Consider ceftolozane-tazobactam, ceftazidime-avibactam, or carbapenems based on susceptibility testing 3
Common Pitfalls to Avoid
Monotherapy for mixed infections: Avoid using gentamicin alone, which is only indicated for uncomplicated UTIs 1
Inadequate dosing: Ensure proper weight-based dosing of gentamicin to achieve therapeutic levels while minimizing toxicity
Fluoroquinolone use: Avoid empiric fluoroquinolone treatment if:
- Local resistance rates are >10%
- Patient has used fluoroquinolones in the last 6 months
- Patient is from a urology department 1
Neglecting underlying factors: Address any urological abnormalities or underlying complicating factors that may contribute to treatment failure 1
Inadequate duration: Ensure complete treatment course to prevent relapse, especially with Pseudomonas infections which have high recurrence rates 4
Once-daily gentamicin dosing has been shown to be as effective as traditional three-times-daily dosing while potentially reducing toxicity 5, making the recommended regimen both effective and relatively safe when properly monitored.