Amikacin Dosing for an 8-Month-Old Infant Weighing 7.8 kg
For this 8-month-old infant weighing 7.8 kg, administer amikacin 58.5 mg (7.5 mg/kg) every 12 hours intravenously or intramuscularly, for a total daily dose of 117 mg (15 mg/kg/day).
Standard Pediatric Dosing Algorithm
The FDA-approved dosing for infants and children with normal renal function is 15 mg/kg/day divided into 2 or 3 equal doses, administered as either 7.5 mg/kg every 12 hours or 5 mg/kg every 8 hours 1.
Weight-Based Calculation for This Patient
- Total daily dose: 7.8 kg × 15 mg/kg/day = 117 mg/day 1
- Divided dosing (preferred): 7.8 kg × 7.5 mg/kg = 58.5 mg every 12 hours 1
- Alternative three-times-daily dosing: 7.8 kg × 5 mg/kg = 39 mg every 8 hours 1
Dosing Frequency Considerations
The twice-daily regimen (7.5 mg/kg every 12 hours) is preferred over three-times-daily dosing for this age group, as it provides adequate therapeutic levels while simplifying administration 1. The IDSA guidelines for infants and children under 5 years of age support 2.5 mg/kg every 8 hours for gentamicin (a related aminoglycoside), but amikacin's longer half-life and dosing characteristics favor the every-12-hour schedule 2.
Treatment Duration and Monitoring
The usual duration of amikacin treatment is 7 to 10 days, and it is desirable to limit treatment to short-term whenever feasible 1.
Therapeutic Drug Monitoring Requirements
- Measure peak serum concentrations 30 to 90 minutes after injection; target levels should not exceed 35 mcg/mL 1
- Measure trough concentrations just prior to the next dose; levels should remain below 10 mcg/mL 1
- Peak concentrations above 35 mcg/mL and trough concentrations above 10 mcg/mL should be avoided to minimize toxicity risk 1
Clinical Response Assessment
If definite clinical response does not occur within 3 to 5 days, therapy should be stopped and antibiotic susceptibility testing should be repeated 1. Uncomplicated infections due to amikacin-sensitive organisms should respond within 24 to 48 hours 1.
Special Considerations for Infants
Amikacin clearance is substantially slower in infants due to immature renal function, which prolongs the drug's half-life 3. This physiologic consideration supports the twice-daily dosing regimen rather than more frequent administration.
Renal Function Monitoring
Assess renal function before initiating therapy by measuring serum creatinine concentration or calculating creatinine clearance 1. Reassess renal function periodically during therapy, as aminoglycosides carry inherent nephrotoxicity risk 1.
Critical Safety Warnings
Amikacin shares with other aminoglycosides the risk of ototoxicity and nephrotoxicity 4. These adverse effects are more likely with:
- Prolonged treatment beyond 10 days 1
- Elevated peak or trough serum concentrations 1
- Concurrent use of other nephrotoxic or ototoxic agents 4
If treatment beyond 10 days is necessary, closely monitor amikacin serum levels and assess renal, auditory, and vestibular functions 1.
Route of Administration
Amikacin may be administered either intramuscularly or intravenously 1. For infants, intravenous administration via short-term infusion (over 30 minutes) is often preferred for ease of administration and to avoid painful intramuscular injections 5.