What is the recommended dosing regimen for amoxicillin (amoxicillin) in adult and pediatric patients with common bacterial infections?

Amoxicillin Dosing Guidelines

Pediatric Dosing (≥3 Months and <40 kg)

For most common bacterial infections in children, amoxicillin should be dosed at 45 mg/kg/day divided every 12 hours for mild-to-moderate infections, and 90 mg/kg/day divided every 12 hours for severe infections or areas with high pneumococcal resistance, with a maximum daily dose of 4000 mg. 1, 2, 3

Indication-Specific Pediatric Dosing:

Respiratory Tract Infections (Pneumonia, Sinusitis):

• Mild-to-moderate: 45 mg/kg/day divided every 12 hours 4, 1, 2
• Severe or high resistance areas: 90 mg/kg/day divided every 12 hours 1, 2, 3
• Duration: 7-10 days for most infections; 10 days specifically for pneumonia 1, 2

Group A Streptococcal Infections (Pharyngitis, Scarlet Fever):

• Dose: 50-75 mg/kg/day divided into 2 doses for 10 days 1, 2
• Maximum per dose: 1000 mg 2
• Critical: Must complete full 10-day course to prevent rheumatic fever 2, 3

Ear/Nose/Throat, Skin, Genitourinary Infections:

• Mild-to-moderate: 25 mg/kg/day divided every 12 hours or 20 mg/kg/day divided every 8 hours 3
• Severe: 45 mg/kg/day divided every 12 hours or 40 mg/kg/day divided every 8 hours 3

Infants <3 Months:

The maximum dose for neonates and infants under 3 months is 30 mg/kg/day divided every 12 hours due to immature renal function. 3

Adult Dosing (≥40 kg)

For adults with common bacterial infections, amoxicillin should be dosed at 500 mg every 12 hours or 250 mg every 8 hours for mild-to-moderate infections, and 875 mg every 12 hours or 500 mg every 8 hours for severe infections. 3

Indication-Specific Adult Dosing:

Respiratory Tract Infections:

• All severities: 875 mg every 12 hours or 500 mg every 8 hours 3

Ear/Nose/Throat, Skin, Genitourinary Infections:

• Mild-to-moderate: 500 mg every 12 hours or 250 mg every 8 hours 3
• Severe: 875 mg every 12 hours or 500 mg every 8 hours 3

Sinusitis:

• Standard dose: 500 mg twice daily 4
• Note: High-dose amoxicillin (875 mg twice daily) does not provide additional benefit over standard dosing for acute sinusitis 5

H. pylori Eradication:

• Triple therapy: 1 gram amoxicillin + 500 mg clarithromycin + 30 mg lansoprazole, all twice daily for 14 days 3
• Dual therapy: 1 gram amoxicillin + 30 mg lansoprazole, both three times daily for 14 days 3

Renal Impairment Dosing

Patients with severe renal impairment require dose reduction, and those with GFR <30 mL/min should NOT receive the 875 mg dose. 3

• GFR 10-30 mL/min: 500 mg or 250 mg every 12 hours 3
• GFR <10 mL/min: 500 mg or 250 mg every 24 hours 3
• Hemodialysis: 500 mg or 250 mg every 24 hours, with additional dose during and at end of dialysis 3

Critical Administration Details

Amoxicillin should be taken at the start of a meal to minimize gastrointestinal intolerance. 3

Treatment duration should be a minimum of 48-72 hours beyond symptom resolution or bacterial eradication. 1, 2, 3

For oral suspension, shake well before each use; reconstituted suspension expires after 14 days (refrigeration preferred but not required). 3

Monitoring and Follow-Up

Children on appropriate antibiotic therapy should demonstrate clinical improvement within 48-72 hours; if no improvement occurs, reevaluation is necessary. 1, 2

Common Pitfalls to Avoid

Twice-daily dosing (every 12 hours) improves adherence compared to three-times-daily regimens and is equally effective for lower respiratory tract infections. 2, 6, 7

Underdosing severe infections or using standard doses in high pneumococcal resistance areas can lead to treatment failure—use 90 mg/kg/day in children or 875 mg twice daily in adults for severe infections. 1, 2

Never use amoxicillin alone for MRSA infections, as it provides no coverage against this pathogen. 2

Adverse Effects

The most common adverse effects include diarrhea, nausea, vomiting, and rash. 1, 3

Hypersensitivity reactions including anaphylaxis can occur; discontinue immediately if serious reactions develop. 3