Gentamicin Dosing for Urinary Tract Infections
For treatment of urinary tract infections, gentamicin should be administered at 5 mg/kg once daily, or alternatively at 3 mg/kg/day divided into three equal doses every 8 hours. 1, 2
Standard Dosing Regimens
Adults
- Once-daily dosing: 5 mg/kg IV/IM once daily 1, 3
- Traditional dosing: 3 mg/kg/day divided into three equal doses (1 mg/kg every 8 hours) 2
- For severe UTIs: Up to 5-7 mg/kg/day may be considered, divided into three doses 2, 3
- Treatment duration: 5-7 days for uncomplicated UTI 3, 1
Children
- Standard dose: 6-7.5 mg/kg/day divided into three doses (2-2.5 mg/kg every 8 hours) 2
- Once-daily option: 4.5-5 mg/kg once daily 4, 5
- Treatment duration: 5-7 days 3
Monitoring Parameters
Therapeutic Drug Monitoring
- Peak serum concentration: Target 4-6 μg/mL (30-60 minutes after IM injection) 2
- Trough serum concentration: Target <1 μg/mL (just before next dose) 2
- Avoid prolonged levels: Keep peak levels below 12 μg/mL 2
Renal Function Monitoring
- Check baseline renal function before initiating therapy
- Monitor serum creatinine regularly during treatment
- For patients with impaired renal function, adjust dosing interval using this formula:
- Interval between doses (hours) = serum creatinine (mg/dL) × 8 2
Dosage Adjustments for Renal Impairment
- CrCl >50 mL/min: No adjustment needed
- CrCl <50 mL/min: Extend dosing interval rather than reduce dose 1, 2
- For severe renal impairment, consider alternative antibiotics
Administration Routes
- IV administration: Dilute single dose in 50-200 mL of sterile isotonic saline or 5% dextrose in water
- Infusion time: Administer over 30 minutes to 2 hours 2
- IM administration: Administer undiluted
Clinical Efficacy
Multiple studies have demonstrated that once-daily dosing is as effective as traditional three-times-daily dosing for UTIs:
- A randomized controlled trial showed 100% microbiological efficacy with both once-daily and three-times-daily regimens 5
- Another study demonstrated successful elimination of bacteriuria in all patients with lower UTI using once-daily dosing 6
Important Considerations and Precautions
- Nephrotoxicity risk: Increases with treatment duration beyond 7 days 1
- Ototoxicity risk: Monitor for hearing changes and vestibular symptoms
- Drug interactions: Avoid concurrent use with other nephrotoxic medications when possible
- Pregnancy: Use only if clearly needed and benefits outweigh risks
Practical Clinical Approach
- Assess infection severity and patient factors
- Choose appropriate dosing regimen based on infection severity and renal function
- Monitor therapeutic levels when feasible, especially in critically ill patients
- Adjust dosing based on clinical response and renal function
- Limit treatment duration to 5-7 days for most UTIs to minimize toxicity risk
Once-daily dosing offers the advantages of reduced nursing time, potentially lower cost, and comparable efficacy to traditional dosing, while potentially reducing nephrotoxicity in patients with normal renal function 4, 5, 7.