Gentamicin Dosing and Duration
For serious infections in adults with normal renal function, administer gentamicin at 3 mg/kg/day divided into three equal doses every 8 hours (1 mg/kg every 8 hours), with treatment duration typically 7-10 days. 1, 2
Standard Dosing by Clinical Indication
Enterococcal Endocarditis (Multiple Divided Dosing Required)
- Administer gentamicin in multiple divided doses totaling 3 mg/kg/day (approximately 1 mg/kg every 8 hours) rather than once-daily dosing 1
- Target 1-hour post-infusion peak concentration of approximately 3 μg/mL and trough concentration <1 μg/mL 1
- Duration depends on symptom duration prior to diagnosis: 1
- Native valve endocarditis with <3 months of symptoms: 4 weeks of therapy
- Native valve endocarditis with ≥3 months of symptoms: 6 weeks of therapy
- Prosthetic valve endocarditis: 6 weeks of therapy
- Short-course gentamicin (2-3 weeks) may be considered in older patients or those at high risk for nephrotoxicity, though this is based on limited evidence 1
Life-Threatening Infections
- Initial dosing up to 5 mg/kg/day may be administered in three or four equal doses 2
- Reduce to 3 mg/kg/day as soon as clinically indicated 2
Urinary Tract Infections (Once-Daily Dosing Acceptable)
- For uncomplicated pyelonephritis requiring hospitalization: 5 mg/kg IV once daily for 5-7 days 3
- This higher dose with once-daily administration is appropriate for UTIs but NOT for endocarditis 3
Critically Ill/Septic Patients
- Initial loading dose should be 7 mg/kg based on total body weight 4, 5
- This accounts for increased volume of distribution in hyperdynamic septic patients 4
Monitoring Requirements
Therapeutic Drug Monitoring (Essential)
- Measure peak concentration 30-60 minutes after infusion completion: 1, 2
- Target: 3-4 μg/mL (up to 6 μg/mL acceptable)
- Avoid prolonged levels >12 μg/mL
- Measure trough concentration just before next dose: 1, 2
- Target: <1 μg/mL
- Avoid levels >2 μg/mL to reduce nephrotoxicity risk
- Perform measurements periodically during therapy, especially in patients with variable pharmacokinetics 5
Renal Impairment Adjustments
Dosing Modifications Required
- Standard 3 mg/kg/day dosing is ONLY for patients with normal renal function 6, 2
- For creatinine clearance <50 mL/min, dose reduction and extended intervals are mandatory 6
Adjustment Methods
- Interval extension method: Multiply serum creatinine (mg/dL) by 8 to determine hours between doses 2
- Example: Creatinine 2.0 mg/dL → give usual dose every 16 hours (2 × 8)
- Dose reduction method: Divide normally recommended dose by serum creatinine level for 8-hour interval dosing 2
- Example: 60 mg normally, creatinine 2.0 mg/dL → give 30 mg every 8 hours
Special Renal Considerations
- Patients with creatinine clearance <20 mL/min should NOT receive 2-week short-course regimens 6
- Consultation with infectious disease or clinical pharmacy is strongly recommended for dose optimization 6
Duration of Therapy
Standard Duration
- Typical treatment course: 7-10 days for most serious infections 2
- Keep treatment duration short (3-5 days) when possible, given aminoglycoside pharmacological properties 4
Extended Duration
- In difficult and complicated infections, longer courses may be necessary 2
- When treatment exceeds 10 days, monitor renal, auditory, and vestibular function closely as toxicity risk increases 2
Special Population Considerations
Obese Patients
- Base dosing on lean body mass or adjusted body weight, not total body weight 2, 5
- Starting dose of 7 mg/kg based on adjusted body weight increases probability of target attainment 5
Pediatric Patients
- Children: 6-7.5 mg/kg/day (2-2.5 mg/kg every 8 hours) 2
- 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
Critical Safety Warnings
Nephrotoxicity Prevention
- Increasing gentamicin dose beyond recommended amounts does NOT enhance efficacy but DOES increase nephrotoxicity risk 1
- TDM targeting trough <0.5-1 mg/mL has proven to reduce nephrotoxicity and is recommended for all patients receiving >1 dose 5
High-Risk Patients
- Older patients, those with pre-existing renal impairment, and debilitated patients are at significantly higher risk for gentamicin-associated complications 1
- In patients with mild renal impairment (creatinine clearance 30-50 mL/min), consider alternative regimens or short-course therapy (2-3 weeks) to minimize nephrotoxicity 1