What is the standard dose and duration of gentamicin (Gentamicin) intramuscularly (IM) for urinary tract infections (UTIs)?

Standard Dose and Duration of Gentamicin IM for UTI

For uncomplicated pyelonephritis requiring hospitalization, administer gentamicin 5 mg/kg IV/IM once daily for 5-7 days; for complicated UTIs or serious infections in adults with normal renal function, use 3 mg/kg/day divided every 8 hours for 7-10 days. 1, 2

Dosing by Clinical Scenario

Uncomplicated Pyelonephritis (Hospitalized Patients)

• 5 mg/kg IV/IM once daily for 5-7 days 1
• This single daily dosing regimen is the guideline-recommended approach per the European Association of Urology 1
• Do NOT use gentamicin as monotherapy—combine with ampicillin or another appropriate agent 1

Serious/Complicated UTIs in Adults

• 3 mg/kg/day divided into three equal doses every 8 hours for 7-10 days 2
• For life-threatening infections, may increase to 5 mg/kg/day in 3-4 divided doses, then reduce to 3 mg/kg/day as soon as clinically indicated 2
• Target peak concentration: 4-6 mcg/mL (measured 30-60 minutes post-IM injection) 2
• Target trough concentration: <2 mcg/mL (measured just before next dose) 2

Pediatric Dosing (Febrile UTI in Infants/Children 2-24 months)

• 7.5 mg/kg/day divided every 8 hours for 7-14 days total therapy 3
• Parenteral therapy should continue until clinical improvement (typically 24-48 hours), then switch to oral agents 3
• Infants and neonates: 7.5 mg/kg/day (2.5 mg/kg every 8 hours) 2
• Premature or full-term neonates ≤1 week: 5 mg/kg/day (2.5 mg/kg every 12 hours) 2

Duration of Therapy

The standard duration is 7-10 days for most UTIs 2. For pediatric febrile UTIs, the total course (parenteral plus oral) should be 7-14 days 3. Courses shorter than 7 days are inferior and should be avoided 3.

Critical Monitoring and Safety Considerations

Therapeutic Drug Monitoring

• Measure peak and trough levels periodically to ensure adequate but not excessive drug levels 2
• Avoid prolonged peak levels >12 mcg/mL 2
• Avoid trough levels >2 mcg/mL 2
• For enterococcal endocarditis (different indication), target trough <1 mcg/mL 4, 5

Renal Impairment Adjustments

• Standard dosing applies ONLY to patients with normal renal function 2
• For creatinine clearance <50 mL/min, dose reduction and extended intervals are mandatory 4
• Interval between doses (hours) ≈ serum creatinine (mg/dL) × 8 2
• Alternatively, divide the normal dose by serum creatinine level for reduced dosing every 8 hours 2
• Do NOT use short-course regimens if creatinine clearance <20 mL/min 4

High-Risk Populations

• Older patients, those with pre-existing renal impairment, and debilitated patients are at significantly higher risk for nephrotoxicity and ototoxicity 4
• In patients with mild renal impairment (CrCl 30-50 mL/min), consider alternative regimens or short-course therapy (2-3 weeks for endocarditis, not UTI) to minimize nephrotoxicity 4
• Patients with extensive burns may have altered pharmacokinetics requiring serum concentration monitoring 2

Common Pitfalls and Caveats

• Dosing in obese patients should be based on lean body mass, not actual body weight 2
• Increasing gentamicin dose beyond recommended amounts does not enhance efficacy but increases nephrotoxicity risk 4, 5
• Gentamicin should NOT be physically premixed with other drugs but administered separately 2
• For lower UTI (uncomplicated cystitis), first-line oral agents (nitrofurantoin, TMP-SMX, fosfomycin) are preferred over parenteral aminoglycosides 1
• Local resistance patterns should guide empirical selection 1
• Treatment duration >10 days requires monitoring of renal, auditory, and vestibular functions due to increased toxicity risk 2

Route of Administration

Both IM and IV routes are acceptable and equally effective 2. For IV administration, dilute single dose in 50-200 mL sterile saline or D5W (less volume for infants/children) and infuse over 0.5-2 hours 2.