Gentamicin Dosing for Urinary Tract Infection
For uncomplicated UTI requiring hospitalization in adults with normal renal function, administer gentamicin 5 mg/kg IV once daily for 5-7 days. 1
Standard Dosing Approach
For urinary tract infections specifically, the evidence supports once-daily dosing rather than divided doses:
- Once-daily dosing of 5 mg/kg IV is the recommended regimen for pyelonephritis requiring hospitalization 1
- This differs from the standard serious infection dosing of 3 mg/kg/day divided every 8 hours, which is reserved for systemic infections like endocarditis 1, 2
- Historical studies demonstrate that single daily doses of 160 mg (approximately 2-3 mg/kg for average adults) successfully eliminated bacteriuria in lower UTIs 3, 4
Dosing Based on Renal Function
Critical distinction: The 5 mg/kg once-daily dose applies ONLY to patients with normal renal function 5, 1
Normal Renal Function (CrCl >50 mL/min):
- 5 mg/kg IV once daily for UTI 1
- Treatment duration: 5-7 days for uncomplicated pyelonephritis 1
- No dose adjustment needed 5
Impaired Renal Function (CrCl <50 mL/min):
- Mandatory dose reduction and extended dosing intervals required 5, 1
- For CrCl 30-50 mL/min: Consider alternative antibiotics or consult infectious disease 1, 6
- For CrCl <20 mL/min: Short-course regimens should NOT be used 1
- Consultation with infectious disease or clinical pharmacy is strongly recommended 5
Monitoring Requirements
Therapeutic drug monitoring is mandatory for all patients receiving more than one dose: 1, 7
- Target trough concentration: <1 mg/L (preferably <0.5 mg/L) to minimize nephrotoxicity 1, 6, 7
- Peak concentration after once-daily dosing: Expected higher peaks (8-12 mcg/mL) are acceptable and desired for efficacy 7
- Monitor renal function at baseline and during therapy 5, 1
Key Safety Considerations
Once-daily dosing is actually LESS nephrotoxic than divided dosing while maintaining equal or superior efficacy:
- A landmark trial showed nephrotoxicity in only 5% with once-daily dosing versus 24% with three-times-daily dosing (p=0.016) 8
- Increasing doses beyond recommended amounts does NOT improve efficacy but significantly increases nephrotoxicity risk 5, 6
- Risk factors for nephrotoxicity include: duration >10 days, baseline renal impairment, advanced age, and concomitant nephrotoxic drugs 1, 2, 7
Common Pitfalls to Avoid
- Do NOT use the 3 mg/kg/day divided dosing (every 8 hours) for simple UTI - this is reserved for endocarditis and other serious systemic infections 1, 6, 2
- Do NOT use once-daily dosing in patients with CrCl <30 mL/min without expert consultation 5, 1
- Do NOT extend treatment beyond 7-10 days without compelling indication as toxicity risk increases substantially 2, 7
- In obese patients, calculate dose based on adjusted body weight, not total body weight 2, 7