What is the recommended dosage of Amoxicillin (Amoxycillin) for adults and children?

Amoxicillin Dosage Recommendations

For adults, the standard amoxicillin dose is 500 mg every 8 hours or 875 mg every 12 hours for most infections, with treatment duration typically 7-10 days; for children over 3 months weighing less than 40 kg, the dose is 20-45 mg/kg/day divided every 8-12 hours depending on infection severity. 1

Adult Dosing Regimens

Standard Infections

• Mild to moderate infections (ear/nose/throat, skin, genitourinary): 500 mg every 12 hours or 250 mg every 8 hours 1
• Severe infections (ear/nose/throat, skin, genitourinary): 875 mg every 12 hours or 500 mg every 8 hours 1
• Lower respiratory tract infections (all severities): 875 mg every 12 hours or 500 mg every 8 hours 1

The FDA label clearly prioritizes the 875 mg twice-daily regimen for respiratory infections and severe infections, which simplifies dosing and improves adherence 1. For sinusitis specifically, amoxicillin is the drug of choice and is generally effective, inexpensive, and well tolerated 2.

Specific Clinical Scenarios

• Acute bacterial sinusitis: Standard amoxicillin dosing for 10-14 days, with assessment at 3-5 days for clinical improvement 2
• Streptococcal pharyngitis: 1000 mg once daily for 10 days is an acceptable alternative to traditional dosing 3
• Erysipeloid (skin infection): 500 mg three times daily for 7-10 days 3
• Community-acquired cutaneous anthrax: 500 mg every 8 hours orally 2

H. pylori Eradication (Adults Only)

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

Pediatric Dosing (Age ≥3 Months and Weight <40 kg)

Weight-Based Dosing

• Mild to moderate infections: 25 mg/kg/day divided every 12 hours OR 20 mg/kg/day divided every 8 hours 1
• Severe infections or lower respiratory tract infections: 45 mg/kg/day divided every 12 hours OR 40 mg/kg/day divided every 8 hours 1

Specific Pediatric Scenarios

• Community-acquired pneumonia: Recent evidence supports 5-day courses as equally effective as 10-day courses for uncomplicated CAP in children 6 months to 10 years 4
• Acute otitis media: High-dose formulation (90 mg/kg/day) may be needed for penicillin-resistant S. pneumoniae 5
• Emergency standby for asplenic children: 50 mg/kg in three divided daily doses 2

Neonates and Infants <3 Months

The maximum dose is 30 mg/kg/day divided every 12 hours due to incompletely developed renal function 1. This is a critical safety consideration that must not be exceeded.

Renal Impairment Dosing

For adults and children >40 kg with severe renal impairment 1:

• GFR 10-30 mL/min: 500 mg or 250 mg every 12 hours (depending on severity)
• 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
• Critical caveat: Patients with GFR <30 mL/min should NOT receive the 875 mg dose 1

Treatment Duration Principles

All streptococcal infections require a minimum 10-day course to prevent acute rheumatic fever, regardless of clinical improvement 1, 2. This is non-negotiable.

For other infections, continue treatment for 48-72 hours beyond symptom resolution or evidence of bacterial eradication 1. Most bacterial infections requiring amoxicillin need 7-10 days of therapy to prevent treatment failure and resistance development 6.

Amoxicillin-Clavulanate (Augmentin) Considerations

When beta-lactamase-producing organisms are suspected:

Adult Dosing

• Standard infections: 500 mg/125 mg twice daily or three times daily 6
• Respiratory infections: 875 mg/125 mg twice daily 6
• Severe infections (IV): 1.2 g every 8 hours 6
• Animal/human bites: 500 mg/125 mg twice daily 6

Pediatric High-Dose Formulation

• 90 mg/kg/day amoxicillin component with 6.4 mg/kg clavulanate, not to exceed 2 g every 12 hours, for resistant organisms 2

Critical warning: Never substitute two 250 mg tablets for one 500 mg tablet when using amoxicillin-clavulanate, as this results in excessive clavulanate dosing and increased gastrointestinal side effects 3, 6.

Administration Guidelines

• Take at the start of a meal to minimize gastrointestinal intolerance 1
• For oral suspension, shake well before each use 1
• Reconstituted suspension must be discarded after 14 days; refrigeration is preferable but not required 1

Common Pitfalls to Avoid

1. Underdosing respiratory infections: Use 875 mg twice daily, not 500 mg, for lower respiratory tract infections 1
2. Stopping treatment early: Complete the full course even if symptoms improve, especially for streptococcal infections 1, 2
3. Ignoring renal function: The 875 mg dose is contraindicated in severe renal impairment 1
4. Inadequate dosing for resistant organisms: Consider high-dose amoxicillin-clavulanate (90/6.4 mg/kg) for suspected resistant pathogens in children 2
5. Switching antibiotics too quickly: Allow 3-5 days to assess clinical response before changing therapy 2