What is the appropriate dosage and treatment duration of amoxicillin for a bacterial respiratory infection?

Amoxicillin Dosage and Duration for Bacterial Respiratory Infections

For bacterial respiratory infections, amoxicillin should be dosed at 875 mg twice daily or 500 mg three times daily for adults, and 45 mg/kg/day divided twice daily or 40 mg/kg/day divided three times daily for children with lower respiratory tract infections, with treatment continuing for 5 days in most cases. 1, 2

Age-Specific Dosing Recommendations

Adults

• Lower respiratory tract infections (pneumonia, bronchitis):
  • 875 mg every 12 hours OR 500 mg every 8 hours 1, 2
  • Total daily dose: 1500-1750 mg
  • Duration: 5 days (minimum) 1

Children (3 months to 12 years)

• Lower respiratory tract infections:
  • 45 mg/kg/day divided every 12 hours OR 40 mg/kg/day divided every 8 hours 1, 2
  • For pneumococcal pneumonia: 80-100 mg/kg/day in three divided doses for children <30 kg 1
  • Duration: 5-10 days (10 days for confirmed pneumococcal pneumonia) 1

Infants (<3 months)

• Maximum dose: 30 mg/kg/day divided every 12 hours 2
• Duration: Minimum 48-72 hours beyond symptom resolution 2

Treatment Duration Based on Infection Type

• Community-acquired pneumonia: Minimum 5 days, extending therapy based on clinical stability (resolution of vital sign abnormalities, ability to eat, and normal mentation) 1
• Pneumococcal pneumonia: 10 days 1
• Atypical pneumonia: 14 days (macrolide preferred) 1
• Bronchitis/COPD exacerbation: 5 days 1
• Streptococcal infections: Minimum 10 days to prevent rheumatic fever 2

Special Considerations

Resistance Patterns

• For suspected penicillin-resistant S. pneumoniae, consider high-dose amoxicillin (3 g/day in adults) 1
• For β-lactamase-producing pathogens (H. influenzae, M. catarrhalis), use amoxicillin-clavulanate instead 1, 3

Renal Impairment

• GFR 10-30 mL/min: 500 mg or 250 mg every 12 hours (based on infection severity) 2
• GFR <10 mL/min: 500 mg or 250 mg every 24 hours 2
• Avoid 875 mg dose in patients with GFR <30 mL/min 2

Treatment Efficacy Assessment

• Evaluate treatment efficacy after 2-3 days 1
• Primary assessment criterion: fever resolution 1
• If no improvement after 48 hours:
  • Consider atypical pathogens (switch to macrolide) 1
  • Reassess diagnosis
  • Consider hospitalization if condition worsens 1

Common Pitfalls to Avoid

1. Inappropriate use for viral infections: Most cases of acute bronchitis are viral and do not require antibiotics 1, 4

2. Underdosing for suspected resistant pathogens: Use higher doses (3 g/day for adults) when S. pneumoniae with decreased penicillin susceptibility is suspected 1

3. Insufficient treatment duration for streptococcal infections: Always treat for at least 10 days to prevent rheumatic fever 2

4. Failure to adjust dose in renal impairment: Reduce dose in severe renal impairment 2

5. Not considering β-lactamase producers: Consider amoxicillin-clavulanate when β-lactamase-producing organisms are suspected 1, 3

Remember that amoxicillin should be taken at the start of a meal to minimize gastrointestinal intolerance 2, and treatment should continue for at least 48-72 hours after the patient becomes asymptomatic 2.