What is the appropriate Augmentin (amoxicillin/clavulanate) dose for a 9‑month‑old infant weighing 9 kg?

Augmentin Dosing for a 9‑Month‑Old Infant Weighing 9 kg

For a 9‑month‑old infant weighing 9 kg, the appropriate Augmentin dose is 405 mg of the amoxicillin component per day, divided into two doses of approximately 202.5 mg each (≈5 mL of the 200 mg/5 mL suspension twice daily), for most respiratory and ear infections. 1, 2

Age and Weight Considerations

• Infants ≥3 months of age may safely receive oral Augmentin when a bacterial infection is suspected or confirmed. 2
• The FDA label specifies that for infants aged 3–12 months, dosing should be based on the amoxicillin component at 30 mg/kg/day divided every 12 hours for standard infections, using the 125 mg/5 mL oral suspension. 3
• However, current pediatric infectious disease guidelines recommend higher doses than the FDA minimum to address contemporary resistance patterns. 1

Standard‑Dose Regimen (45 mg/kg/day)

• For mild to moderate respiratory tract infections (including community‑acquired pneumonia, acute otitis media, or sinusitis) in infants without high‑risk factors, the recommended dose is 45 mg/kg/day of the amoxicillin component, divided into two doses. 1, 2
• Calculation for a 9 kg infant:
  • 45 mg/kg/day × 9 kg = 405 mg total daily dose
  • Divided twice daily = 202.5 mg per dose (approximately 5 mL of 200 mg/5 mL suspension or 2.5 mL of 400 mg/5 mL suspension twice daily). 1, 2
• This standard‑dose regimen provides adequate coverage for penicillin‑susceptible Streptococcus pneumoniae, non–β‑lactamase‑producing Haemophilus influenzae, and Moraxella catarrhalis. 1

High‑Dose Regimen (90 mg/kg/day)

Use the high‑dose regimen (90 mg/kg/day) if ANY of the following risk factors are present:

• Age < 2 years (which applies to this 9‑month‑old infant if other risk factors coexist) 1, 2
• Daycare attendance 1, 2
• Recent antibiotic use within the past 30 days 1, 2
• Incomplete Haemophilus influenzae type b vaccination (fewer than 3 doses) 2
• Residence in an area with >10% penicillin‑resistant S. pneumoniae 1, 2
• Moderate‑to‑severe illness at presentation 1, 2
• Concurrent purulent acute otitis media or purulent conjunctivitis (otitis‑conjunctivitis syndrome) 1, 2
• Treatment failure after 48–72 hours on amoxicillin alone 1, 2

High‑Dose Calculation for a 9 kg Infant

• 90 mg/kg/day × 9 kg = 810 mg total daily dose
• Divided twice daily = 405 mg per dose (approximately 10 mL of 200 mg/5 mL suspension or 5 mL of 400 mg/5 mL suspension twice daily). 1, 2
• The high‑dose formulation provides a 14:1 ratio of amoxicillin to clavulanate (90 mg/kg amoxicillin + 6.4 mg/kg clavulanate), which achieves middle‑ear and sinus fluid concentrations sufficient to overcome penicillin‑resistant S. pneumoniae (MIC up to 2–4 mg/L) and β‑lactamase‑producing H. influenzae and M. catarrhalis. 1, 2, 4, 5

Formulation Selection

• For infants <12 weeks (3 months): The FDA recommends the 125 mg/5 mL suspension because experience with the 200 mg/5 mL formulation is limited in this age group. 3
• For infants ≥3 months: Either the 200 mg/5 mL or 400 mg/5 mL suspension may be used, depending on the prescribed dose. 3
• The 200 mg/5 mL suspension is often preferred for standard‑dose regimens in younger infants to allow more precise volume measurement. 1, 2
• The 400 mg/5 mL suspension is useful for high‑dose regimens to reduce the volume administered per dose. 1, 2

Treatment Duration

• Acute otitis media: 10 days of therapy is recommended for infants and children <2 years. 1, 2, 3
• Community‑acquired pneumonia: 10 days of therapy, continuing for at least 48–72 hours after complete resolution of fever and respiratory symptoms. 1, 2
• Acute bacterial sinusitis: Continue for 7 days after symptom resolution, with a minimum total of 10 days. 1

Monitoring and Expected Response

• Clinical improvement (reduced fever, improved feeding, decreased irritability) should be evident within 48–72 hours of initiating appropriate therapy. 1, 2
• If no improvement or clinical worsening occurs after 48–72 hours:
  • Reassess the diagnosis clinically. 1, 2
  • Consider switching to the high‑dose regimen if standard‑dose was initially used. 1, 2
  • Evaluate for atypical pathogens (Mycoplasma, Chlamydophila) and consider adding a macrolide. 1
  • Obtain further diagnostic imaging or specialist consultation. 1

Common Pitfalls to Avoid

• Underdosing: Using the outdated FDA minimum of 30 mg/kg/day fails to achieve adequate tissue concentrations against contemporary resistant pathogens; current guidelines recommend 45–90 mg/kg/day. 1, 3
• Formulation confusion: Verify the suspension concentration (125/31,200/28.5, or 400/57 mg per 5 mL) before calculating the volume to dispense. 2, 3
• Incorrect substitution: Do not substitute two 250 mg/125 mg tablets for one 500 mg/125 mg tablet, as the clavulanate content differs. 3
• Premature discontinuation: Complete the full 10‑day course even if symptoms improve earlier, to prevent relapse and reduce resistance. 1, 2
• Ignoring risk factors: Failing to escalate to the high‑dose regimen when risk factors for resistant organisms are present leads to treatment failure. 1, 2

Adverse Effects

• The most common adverse effect is diarrhea, occurring in approximately 7–11% of children on standard formulations and 9–10% on high‑dose formulations. 1, 4, 6, 7
• Twice‑daily dosing is associated with significantly less diarrhea than three‑times‑daily dosing (7.2% vs. 10.7% in one trial). 6, 7
• Diaper dermatitis may occur in up to 51% of infants on high‑dose therapy (vs. 35% on placebo). 2
• Other mild adverse effects include nausea, vomiting, and rash. 1, 2

Maximum Dose Limits

• Maximum single dose: 2,000 mg of amoxicillin per administration (not applicable to this 9 kg infant). 2
• Maximum daily dose: 4,000 mg of amoxicillin per day (not applicable to this 9 kg infant). 1, 2

Special Populations

• Renal impairment: Dose adjustment is not required unless renal function is severely impaired (GFR <30 mL/min), which is rare in otherwise healthy infants. 3
• Penicillin allergy: For non‑anaphylactic reactions, second‑ or third‑generation cephalosporins (cefdinir, cefuroxime) are safe alternatives; for IgE‑mediated reactions, use clindamycin or azithromycin. 1, 2