What is the recommended dosage of injectable Gentamicin for treating severe infections?

Injectable Gentamicin Dosage for Severe Infections

For adults with normal renal function and severe infections, administer gentamicin 3 mg/kg/day divided into three equal doses every 8 hours, targeting peak levels of 3-4 μg/mL and trough levels <1 μg/mL. 1, 2, 3

Standard Dosing by Patient Population

Adults with Normal Renal Function

• Standard dose: 3 mg/kg/day divided every 8 hours (1 mg/kg per dose) 3, 1
• Life-threatening infections: May increase to 5 mg/kg/day divided every 6-8 hours, but reduce to 3 mg/kg/day as soon as clinically indicated 3
• Critical illness/sepsis: Consider 7 mg/kg as a single loading dose, particularly in hyperdynamic septic patients with increased volume of distribution 4, 5

Pediatric Patients

• Children: 6-7.5 mg/kg/day (2-2.5 mg/kg every 8 hours) 3
• Infants and neonates: 7.5 mg/kg/day (2.5 mg/kg every 8 hours) 3
• Premature/full-term neonates ≤1 week: 5 mg/kg/day (2.5 mg/kg every 12 hours) 3

Target Serum Concentrations

Therapeutic Monitoring Parameters

• Peak levels (measured 30-60 minutes post-infusion): 3-4 μg/mL for synergistic therapy (endocarditis), 4-6 μg/mL for standard infections 1, 3
• Trough levels (immediately before next dose): <1 μg/mL (mandatory to minimize nephrotoxicity and ototoxicity) 1, 2, 3
• Avoid: Prolonged peak levels >12 μg/mL and trough levels >2 μg/mL 3

Renal Impairment Dosing

Dose Adjustment Algorithm

• CrCl >100 mL/min: 100% of usual dose every 8 hours 3
• CrCl 70-100 mL/min: 80% of usual dose every 8 hours 3
• CrCl 55-70 mL/min: 65% of usual dose every 8 hours 3
• CrCl 45-55 mL/min: 55% of usual dose every 8 hours 3
• CrCl 40-45 mL/min: 50% of usual dose every 8 hours 3
• CrCl <20 mL/min: Two-week gentamicin regimens are contraindicated; mandatory specialist consultation required 1

Practical Dosing Interval Adjustment

• Simplified method: Multiply serum creatinine (mg/dL) by 8 to determine dosing interval in hours 3
  • Example: Creatinine 2.0 mg/dL → dose every 16 hours
• Alternative method: Divide normal dose by serum creatinine level for reduced dose every 8 hours 3
  • Example: 60 mg normal dose ÷ creatinine 2.0 = 30 mg every 8 hours

Administration Routes

Intravenous Administration

• Dilution: 50-200 mL sterile normal saline or D5W for adults; use smaller volumes for pediatrics 3
• Infusion time: 30 minutes to 2 hours 3
• Never premix with other drugs; administer separately 3

Intramuscular Administration

• Acceptable alternative route with identical dosing to IV 3
• May be preferred in patients with difficult IV access 3

Special Clinical Contexts

Endocarditis Treatment

• Dosing: 3-6 mg/kg/day divided every 8 hours for synergistic effect 6, 1
• Duration: First 2 weeks for streptococcal infections; entire course for enterococcal infections 6
• Critical: Multiple daily dosing is mandatory—once-daily dosing is contraindicated for endocarditis 1, 2

Critically Ill/Septic Patients

• Loading dose: 7 mg/kg recommended due to significantly increased volume of distribution 4, 5
• Female patients: Require particular attention as they demonstrate higher volume of distribution (0.50 vs 0.40 L/kg) and lower peak concentrations despite equivalent mg/kg dosing 7
• Monitoring: More frequent serum level checks essential due to unpredictable pharmacokinetics 5

Obese Patients

• Dosing weight: Use adjusted body weight or lean body mass, not total body weight 3, 5

Mandatory Therapeutic Drug Monitoring

When to Monitor

• All patients receiving gentamicin require serum level monitoring 1, 2
• Frequency: Peak and trough levels measured intermittently during therapy 3
• Renal function: Monitor serum creatinine at least weekly 1

High-Risk Populations Requiring Intensive Monitoring

• CrCl <50 mL/min 1
• Critically ill patients 5
• Elderly patients 5
• Pediatric and neonatal patients 5
• Patients on intermittent hemodialysis 5
• Patients receiving concomitant nephrotoxic drugs (NSAIDs, vancomycin) 1

Treatment Duration

• Standard: 7-10 days for most infections 3
• Extended therapy: If required beyond 10 days, monitor renal, auditory, and vestibular function closely as toxicity risk increases significantly 3
• Short-term use: Limit to 3-5 days when possible, considering aminoglycosides' poor tissue penetration 4

Critical Safety Considerations

Nephrotoxicity Prevention

• Trough monitoring: Target <0.5-1 mg/L (not just <2 mg/L) to reduce nephrotoxicity 5
• Avoid concomitant nephrotoxins: NSAIDs, vancomycin, and other nephrotoxic agents increase risk 1
• Dose reduction: Mandatory with any decline in renal function, as gentamicin accumulates rapidly 1

Ototoxicity Risk

• Increases with treatment duration >10 days 3
• Monitor auditory and vestibular function in prolonged therapy 3

Common Pitfalls to Avoid

1. Never use once-daily dosing for endocarditis—multiple daily dosing is required for synergistic bactericidal effect 1, 2
2. Do not use standard dosing in declining renal function—gentamicin accumulates rapidly and toxicity is concentration-dependent 1
3. Do not underdose critically ill patients—use 7 mg/kg loading dose due to increased volume of distribution 4, 5
4. Do not dose obese patients on total body weight—use adjusted body weight 3, 5
5. Do not extend therapy beyond necessary duration—toxicity risk increases significantly after 10 days 3

Mandatory Specialist Consultation

Consult infectious disease, clinical pharmacy, or nephrology for: 1

• CrCl <50 mL/min requiring gentamicin therapy
• Rapidly declining renal function during treatment
• Failure to achieve target levels despite dose adjustments
• Oliguric/anuric patients or rapidly decreasing renal function on high-dose regimens 4