What is the proper dosage of amoxicillin (amoxicillin) for a 6.6kg patient with a lower respiratory tract infection?

Amoxicillin Dosing for 6.6kg Patient with Lower Respiratory Tract Infection

For a 6.6kg infant with a lower respiratory tract infection, administer amoxicillin 297 mg divided every 12 hours (148.5 mg per dose) for 7-10 days.

Dosing Calculation

• For infants under 3 months (less than 12 weeks): The FDA label specifies a maximum dose of 30 mg/kg/day divided every 12 hours due to incompletely developed renal function 1

• For infants 3 months and older with lower respiratory tract infection: The recommended dose is 45 mg/kg/day divided every 12 hours (or 40 mg/kg/day divided every 8 hours) for mild to severe infections 1

• Age-appropriate dosing for this patient:

  • If under 3 months: 30 mg/kg/day = 198 mg/day divided every 12 hours = 99 mg per dose twice daily 1
  • If 3 months or older: 45 mg/kg/day = 297 mg/day divided every 12 hours = 148.5 mg per dose twice daily 1

Critical Age Determination

You must determine if this infant is younger or older than 3 months (12 weeks), as this fundamentally changes the dosing regimen. The weight of 6.6kg could represent either age group, making clinical assessment essential 1.

Practical Administration

• Using 125 mg/5 mL suspension:

  • For under 3 months: Give approximately 4 mL twice daily (99 mg per dose) 1
  • For 3 months or older: Give approximately 6 mL twice daily (148.5 mg per dose) 1

• Administer at the start of meals to minimize gastrointestinal intolerance 1

• Can be mixed with formula, milk, fruit juice, or water and given immediately 1

Duration of Treatment

• Continue for minimum 48-72 hours beyond symptom resolution or evidence of bacterial eradication 1

• Standard duration is 7-10 days for lower respiratory tract infections 2

• If Streptococcus pyogenes is suspected, treat for at least 10 days to prevent acute rheumatic fever 1

Clinical Monitoring

• Assess response at 48-72 hours 3, 4

• If no improvement or worsening occurs, consider:

  • Switching to high-dose amoxicillin-clavulanate (90 mg/6.4 mg per kg per day) 4
  • Reevaluation for complications or alternative diagnoses 3, 4
  • Parenteral therapy with ceftriaxone if severe 4

Important Caveats

• Plain amoxicillin may have limited efficacy in lower respiratory tract infections when pneumonia is not suspected, with studies showing minimal benefit over placebo in older children 5, 6

• Consider amoxicillin-clavulanate instead if there is:

  • Recent antibiotic use (within 30 days) 4
  • Risk factors for β-lactamase-producing organisms (H. influenzae, M. catarrhalis) 3, 4
  • Insufficient vaccination against H. influenzae type b 3

• For amoxicillin-clavulanate dosing in this weight range: 90 mg/kg/day of amoxicillin component (594 mg/day) with 6.4 mg/kg/day clavulanate, divided every 12 hours 3, 4

• Refrigeration of reconstituted suspension is preferable but not required; discard after 14 days 1