Amoxicillin Dosing for Lower Respiratory Tract Infections
For adults with lower respiratory tract infections, amoxicillin should be dosed at 500-1000 mg every 8 hours orally, or alternatively 875 mg every 12 hours, with treatment duration of at least 7 days. 1, 2
Adult Dosing Recommendations
Standard Dosing
- Mild to moderate infections: 500 mg every 12 hours OR 250 mg every 8 hours 2
- Severe infections or lower respiratory tract involvement: 875 mg every 12 hours OR 500 mg every 8 hours 1, 2
- The European Respiratory Society guidelines specifically recommend 500-1000 mg every 8 hours for community-acquired lower respiratory tract infections managed in hospital settings 1
Treatment Duration
- Minimum duration: At least 7 days for most lower respiratory tract infections 1
- Continue therapy for 48-72 hours beyond symptom resolution or evidence of bacterial eradication 2
- For Streptococcus pyogenes infections: minimum 10 days to prevent acute rheumatic fever 2
- For Legionella pneumophila: 21 days of treatment 1
Pediatric Dosing (≥3 months and <40 kg)
Lower Respiratory Tract Infections
- Mild, moderate, or severe: 45 mg/kg/day in divided doses every 12 hours OR 40 mg/kg/day in divided doses every 8 hours 2
- For children <3 years with pneumonia: 80-100 mg/kg/day in three daily doses (for children <30 kg) 1
Infants <3 months
- Maximum dose: 30 mg/kg/day divided every 12 hours due to immature renal function 2
Renal Impairment Adjustments
Severe renal impairment requires dose reduction 2:
- GFR 10-30 mL/min: 500 mg or 250 mg every 12 hours
- GFR <10 mL/min: 500 mg or 250 mg every 24 hours
- Hemodialysis: 500 mg or 250 mg every 24 hours, with additional dose during and at end of dialysis
- Important caveat: Patients with GFR <30 mL/min should NOT receive the 875 mg dose 2
Alternative Formulations for Resistant Pathogens
When dealing with drug-resistant Streptococcus pneumoniae (penicillin MIC 4-8 mg/L), consider amoxicillin/clavulanate 2000/125 mg every 12 hours, which has demonstrated 95-98% clinical success rates against penicillin-resistant strains 1, 3. This formulation provides adequate amoxicillin levels throughout the dosing interval to eradicate resistant organisms 3.
Administration Considerations
- Take at the start of meals to minimize gastrointestinal intolerance 2
- For oral suspension: shake well before each use and refrigerate (though not required) 2
- Assess clinical response at day 5-7 for improvement of symptoms 1
Clinical Context
The choice between every-8-hour and every-12-hour dosing depends on infection severity. Research demonstrates that 875/125 mg every 12 hours is as effective as 500/125 mg every 8 hours for lower respiratory tract infections, with potentially less diarrhea 4. However, for hospitalized patients or severe infections, the European guidelines favor the every-8-hour regimen at higher individual doses 1.