Daily Maximum Dose of Amoxicillin
The maximum daily dose of amoxicillin is 4 grams (4000 mg) per day for both adults and children, regardless of body weight or size. 1, 2
Adult Maximum Dosing
- The absolute ceiling is 4 grams per day for oral amoxicillin, which applies universally regardless of patient weight or infection severity 1
- When combined with clavulanic acid (amoxicillin-clavulanate), the maximum remains 4 grams of the amoxicillin component per day 1
- The FDA label confirms standard adult dosing ranges from 250-500 mg every 8 hours or 500-875 mg every 12 hours, with the upper limit not exceeding 4 grams daily 2
Pediatric Maximum Dosing
- For children, high-dose amoxicillin is defined as 90 mg/kg/day, but must not exceed 4000 mg/day 1
- For infants less than 3 months (12 weeks) old, the maximum is lower at 30 mg/kg/day divided every 12 hours due to immature renal function 2
- For Group A streptococcal pharyngitis specifically, the maximum is 50 mg/kg once daily (capped at 1000 mg) or 25 mg/kg twice daily (capped at 500 mg per dose) 3
- For Haemophilus influenzae pneumonia, dosing ranges from 75-100 mg/kg/day in children, but the 4-gram daily maximum still applies 3
Critical Clinical Considerations
A common pitfall is assuming larger or obese patients can receive doses exceeding 4 grams per day—this is incorrect. 1 The 4-gram maximum is absolute and based on gastrointestinal tolerability rather than toxicity concerns 1.
Weight-Based Dosing Challenges
- Primary care physicians frequently underdose older, heavier children when the calculated dose (80-90 mg/kg/day) would exceed adult maximum dosing 4
- When a child's weight-based calculation exceeds 4 grams daily, prescribe the standard adult maximum of 4 grams rather than the calculated pediatric dose 1, 4
- This issue was not specifically addressed during guideline formulation, leading to varied prescribing practices 4
Important Distinctions
- Do not confuse oral amoxicillin limits with intravenous ampicillin dosing, which can reach 12 grams daily for severe infections like endocarditis 1
- For severe pneumonia in children requiring high-dose therapy, ampicillin can be dosed at 300-400 mg/kg/day intravenously, but this does not apply to oral amoxicillin 3