What is the recommended dose of amoxicillin (amoxicillin) for a patient with Lower Respiratory Tract Infection (LRTI), considering factors such as age, weight, renal function (Impaired renal function), and severity of infection?

Amoxicillin Dosing for Lower Respiratory Tract Infection

For adults and children ≥3 months weighing ≥40 kg with LRTI, the recommended dose is 875 mg every 12 hours or 500 mg every 8 hours, with the higher dose preferred for moderate to severe infections. 1

Standard Dosing by Age and Weight

Adults and Children ≥40 kg

• Lower respiratory tract infections (mild, moderate, or severe): 875 mg every 12 hours OR 500 mg every 8 hours 1
• The 875 mg twice-daily regimen is equally effective as 500 mg three times daily and offers better compliance with similar or fewer gastrointestinal side effects 2
• Treatment duration: minimum 48-72 hours beyond symptom resolution or bacterial eradication 1

Children ≥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 1
• This applies regardless of severity for lower respiratory tract infections in children 1

Infants <3 Months (12 weeks)

• Maximum dose: 30 mg/kg/day divided every 12 hours due to immature renal function 1
• No specific dosing recommendations exist for infants with renal impairment 1

Dosing Adjustments for Impaired Renal Function

Critical caveat: Patients with GFR <30 mL/min should NOT receive the 875 mg dose 1

Severe Renal Impairment Dosing (Adults and Children >40 kg)

• GFR 10-30 mL/min: 500 mg or 250 mg every 12 hours (depending on infection severity) 1
• GFR <10 mL/min: 500 mg or 250 mg every 24 hours (depending on infection severity) 1
• Hemodialysis: 500 mg or 250 mg every 24 hours, with an additional dose during and at the end of dialysis 1

Clinical Context and Guideline Recommendations

Amoxicillin is recommended as first-line therapy for community-acquired LRTI in primary care settings 3. The European Respiratory Society guidelines identify amoxicillin (along with tetracyclines) as the preferred first-choice antibiotic for all community-acquired LRTIs and mild hospital-acquired COPD exacerbations 3.

When Amoxicillin is Appropriate

• Community-acquired LRTI without suspected pneumonia 3
• Mild COPD exacerbations in hospitalized patients 3
• Selected cases with specific risk factors (age >75 years with fever, cardiac failure, insulin-dependent diabetes, serious neurological disorders) 3

Important Limitations

Recent high-quality evidence challenges routine amoxicillin use: A large randomized controlled trial (n=2,061) found that amoxicillin provided no significant benefit over placebo for symptom duration in adults with acute LRTI when pneumonia was not suspected, including in patients ≥60 years old 4. Similarly, a pediatric trial (n=432) showed no benefit in children aged 6 months to 12 years with uncomplicated LRTI 5.

These findings suggest amoxicillin should be reserved for:

• Suspected or confirmed pneumonia 3
• COPD exacerbations with all three cardinal symptoms (increased dyspnea, sputum volume, and purulence) 3
• High-risk patients with specific comorbidities 3

Administration Instructions

• Take at the start of a meal to minimize gastrointestinal intolerance 1
• Oral suspension must be shaken well before each use 1
• Reconstituted suspension expires after 14 days; refrigeration preferred but not required 1

Monitoring and Follow-up

• Clinical improvement should be evident within 3 days 3
• Patients should return if symptoms persist beyond 3 weeks 3
• High-risk patients (fever, tachypnea, dyspnea, comorbidities, age >65 years) require reassessment at 2 days 3