Amoxicillin Dosing for 3-Month-Old Infant with Acute Otitis Media
For a 3-month-old infant with acute otitis media using the 125 mg/5 mL formulation, administer 40 mg/kg/day divided into two doses (every 12 hours), which translates to the volume in mL based on the infant's weight.
Dosing Calculation Algorithm
Step 1: Determine the Appropriate Dose
- For infants ≥3 months with acute otitis media, the recommended dose is 40 mg/kg/day divided every 12 hours 1
- The WHO Pocket Book recommends amoxicillin 40 mg/kg/day in two divided doses (BD) for 5 days for acute otitis media 1
- The FDA label confirms 25 mg/kg/day divided every 12 hours for mild/moderate infections or 45 mg/kg/day divided every 12 hours for severe infections in children ≥3 months 2
Step 2: Calculate Daily Dose in mg
- Multiply the infant's weight in kg by 40 mg to get the total daily dose 1
- Divide this total by 2 to get the dose per administration (given every 12 hours) 1
Step 3: Convert mg to mL Using 125 mg/5 mL Formulation
- Formula: (Dose in mg ÷ 125 mg) × 5 mL = Volume in mL per dose 2
- For total daily volume: multiply the per-dose volume by 2 2
Example Calculation
For a 6 kg infant:
- Total daily dose: 6 kg × 40 mg/kg = 240 mg/day
- Per-dose amount: 240 mg ÷ 2 = 120 mg per dose
- Volume per dose: (120 mg ÷ 125 mg) × 5 mL = 4.8 mL per dose
- Total daily volume: 4.8 mL × 2 = 9.6 mL/day
Treatment Duration and Administration
- Continue treatment for 5 days minimum 1
- Administer at the start of a meal to minimize gastrointestinal intolerance 2
- Shake the oral suspension well before each use 2
- Store reconstituted suspension in refrigerator (preferable but not required) and discard after 14 days 2
Critical Dosing Considerations for This Age Group
Upper Dose Limitation
- For infants <12 weeks (3 months), the maximum recommended dose is 30 mg/kg/day divided every 12 hours due to incompletely developed renal function 2
- Since this patient is exactly 3 months old, confirm the infant is ≥12 weeks of age before using the 40 mg/kg/day dose 2
- If the infant is <12 weeks, reduce to 30 mg/kg/day divided every 12 hours 2
When to Consider Higher Doses
- High-dose amoxicillin (80-90 mg/kg/day) is NOT typically recommended for first-line treatment in infants at low risk for resistant bacteria 3, 4
- Reserve high-dose regimens for treatment failures or when drug-resistant Streptococcus pneumoniae is suspected 5
- Children who have received antibiotics in the previous 30 days or have otitis-conjunctivitis may require high-dose amoxicillin-clavulanate instead 6
Common Pitfalls to Avoid
- Do not use the 875 mg tablet formulation in infants - only oral suspension is appropriate 2
- Do not underdose based on age-band dosing - weight-based dosing (mg/kg) is essential for accurate dosing in infants 1
- Avoid prescribing without confirming adequate visualization of the tympanic membrane, as diagnosis of AOM in infants can be challenging 1
- For children <2 years of age, antibiotic therapy is recommended (Grade A evidence) rather than watchful waiting 1
Clinical Reassessment
- Evaluate clinical response within 48-72 hours of initiating therapy 6
- If no improvement or worsening occurs, consider treatment failure and switch to amoxicillin-clavulanate or second-generation cephalosporin 1
- The predominant pathogens in treatment failures are beta-lactamase-producing Haemophilus influenzae (62% failure rate with standard amoxicillin) 5