Recommended Intramuscular (IM) Dose of Gentamicin
The recommended intramuscular (IM) dose of gentamicin for adults with normal renal function is 3 mg/kg/day divided into 2 or 3 equally divided doses. 1
Adult Dosing Guidelines
- For serious infections in adults with normal renal function, the standard IM dose is 3 mg/kg/day divided into three equal doses (1 mg/kg every 8 hours) 1
- For life-threatening infections, dosages up to 5 mg/kg/day may be administered in three or four equal doses, but should be reduced to 3 mg/kg/day as soon as clinically indicated 1
- When used specifically for prosthetic valve endocarditis caused by staphylococci, gentamicin is dosed at 3 mg/kg/day IV/IM in 2 or 3 equally divided doses for 2 weeks 2
- For enterococcal endocarditis, gentamicin is administered at 3 mg/kg/day IV/IM in 3 equally divided doses for 4-6 weeks 2
Pediatric Dosing Guidelines
- For children: 6 to 7.5 mg/kg/day (2 to 2.5 mg/kg administered every eight hours) 1
- For infants and neonates: 7.5 mg/kg/day (2.5 mg/kg administered every eight hours) 1
- For premature or full-term neonates one week of age or less: 5 mg/kg/day (2.5 mg/kg administered every 12 hours) 1
- For pediatric patients with UTI, gentamicin should be dosed at 3 mg/kg/day divided into three equal doses 3
Monitoring and Safety Considerations
- It is desirable to measure both peak and trough serum concentrations of gentamicin to determine the adequacy and safety of the dosage 1
- Peak concentration (30-60 minutes after IM injection) should be in the range of 4-6 mcg/mL, and dosage should be adjusted to avoid prolonged levels above 12 mcg/mL 1
- Trough concentrations (just before next dose) should be kept below 2 mcg/mL 1
- For patients with renal impairment, dosage adjustment is necessary - the interval between doses (in hours) may be approximated by multiplying the serum creatinine level (mg/100 mL) by 8 1
Duration of Treatment
- The usual duration of treatment for most infections is 7-10 days 1
- For complicated infections requiring longer therapy, monitoring of renal, auditory, and vestibular functions is recommended, as toxicity is more likely with treatment extended beyond 10 days 1
Special Considerations
- The dosage of gentamicin in obese patients should be based on an estimate of lean body mass rather than total body weight 1
- In patients with extensive burns, altered pharmacokinetics may result in reduced serum concentrations of aminoglycosides, requiring measurement of serum concentrations for dosage adjustment 1
- Recent research suggests that a higher starting dose of 7 mg/kg (based on total body weight or adjusted body weight in obese patients) may be optimal for increasing the probability of target attainment after the first administration 4
- IM administration may result in erratic absorption in infants and children, which should be considered when choosing this route 5
Route Selection Considerations
- IV administration may be particularly useful for treating patients with bacterial septicemia, shock, congestive heart failure, hematologic disorders, severe burns, or reduced muscle mass 1
- When choosing between IM and IV routes, consider safety, efficacy, patient preference, and pharmacoeconomics 6
By following these dosing guidelines and monitoring parameters, clinicians can optimize gentamicin therapy while minimizing the risk of toxicity.