Amoxicillin Dosing Guidelines
Adult Dosing
For adults with common bacterial infections, amoxicillin dosing ranges from 500 mg every 12 hours for mild infections to 875 mg every 12 hours for severe infections, with treatment duration typically 7-10 days depending on the infection type. 1
Standard Adult Regimens by Severity
- 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
Special Adult Indications
- H. pylori triple therapy: 1 gram amoxicillin twice daily (every 12 hours) for 14 days, combined with 500 mg clarithromycin and 30 mg lansoprazole 1
- H. pylori dual therapy: 1 gram amoxicillin three times daily (every 8 hours) for 14 days, combined with 30 mg lansoprazole 1
Renal Impairment Adjustments (Adults)
- 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 1
- Hemodialysis: 500 mg or 250 mg every 24 hours, with an additional dose during and at the end of dialysis 1
- Critical caveat: The 875 mg dose should NOT be used in patients with GFR <30 mL/min 1
Pediatric Dosing (≥3 Months and <40 kg)
For pediatric patients 3 months and older weighing less than 40 kg, amoxicillin dosing is weight-based: 25 mg/kg/day divided every 12 hours for mild infections and 45 mg/kg/day divided every 12 hours for severe infections or respiratory tract infections. 2, 3
Standard Pediatric Regimens by Severity
- Mild to moderate infections (ear/nose/throat, skin, genitourinary): 25 mg/kg/day divided every 12 hours OR 20 mg/kg/day divided every 8 hours 1
- Severe infections (ear/nose/throat, skin, genitourinary): 45 mg/kg/day divided every 12 hours OR 40 mg/kg/day divided every 8 hours 1
- Lower respiratory tract infections (all severities): 45 mg/kg/day divided every 12 hours OR 40 mg/kg/day divided every 8 hours 1
High-Dose Regimens for Resistant Pathogens
- Community-acquired pneumonia in high-resistance areas: 90 mg/kg/day divided every 12 hours, maximum 4000 mg/day 2, 3
- This higher dose is specifically indicated when pneumococcal resistance is suspected or documented 2
Specific Pediatric Indications
- Group A Streptococcal infections (including scarlet fever): 50-75 mg/kg/day divided into 2 doses for 10 days, not exceeding 1000 mg per dose 2, 3
- The 10-day duration is mandatory to prevent acute rheumatic fever 3
Infant Dosing (<3 Months)
For infants younger than 3 months, the maximum recommended dose is 30 mg/kg/day divided every 12 hours due to immature renal function. 1
- Upper dose limit: 30 mg/kg/day divided every 12 hours 1
- This reduced dosing accounts for incompletely developed renal function affecting amoxicillin elimination 1
- For severe infections in infants: Consider 45 mg/kg/day divided every 12 hours for those 3 months and older 2
Critical Treatment Duration Guidelines
- Minimum duration: Continue treatment for 48-72 hours beyond symptom resolution or bacterial eradication 1
- Streptococcal infections: Minimum 10 days required to prevent acute rheumatic fever 1, 3
- Most respiratory infections: 7-10 days, with pneumonia specifically requiring 10 days 2, 3
- H. pylori eradication: 14 days for both triple and dual therapy 1
Administration and Monitoring
Administration Guidelines
- Take at the start of a meal to minimize gastrointestinal intolerance 1
- Twice-daily dosing improves adherence compared to three-times-daily regimens 3
- Shake oral suspension well before each use 1
- Refrigeration of reconstituted suspension is preferable but not required; discard after 14 days 1
Expected Clinical Response
- Clinical improvement should occur within 48-72 hours of starting treatment 2, 3
- If no improvement by 72 hours, reassess diagnosis and consider alternative antibiotics 3
- Patients with streptococcal infections become non-contagious after 24 hours of therapy 3
Common Pitfalls and Caveats
Dosing Errors to Avoid
- Never substitute two 250 mg tablets for one 500 mg tablet when using amoxicillin-clavulanate, as this results in excessive clavulanate dosing 4
- Do not use 875 mg dose in patients with severe renal impairment (GFR <30 mL/min) 1
- Ensure weight-based dosing in pediatrics does not exceed maximum adult doses 2, 3
Resistance Considerations
- Amoxicillin alone is ineffective against MRSA; alternative antibiotics must be used if MRSA is suspected or confirmed 3
- For β-lactamase-producing organisms (H. influenzae, M. catarrhalis), amoxicillin-clavulanate is required rather than amoxicillin alone 2
- In areas with high pneumococcal resistance, use 90 mg/kg/day dosing for pediatric respiratory infections 2
Adverse Effects
- Most common: Diarrhea, nausea, vomiting, and rash (>1% incidence) 1, 3
- Hypersensitivity reactions: Rash, urticaria, and rarely anaphylaxis may occur 3
- Monitor for Clostridioides difficile-associated diarrhea, especially with prolonged courses 1
Drug Interactions
- Coadministration with allopurinol increases rash risk 1
- May reduce efficacy of oral contraceptives; advise backup contraception 1
- Concomitant use with oral anticoagulants may prolong prothrombin time; monitor INR 1
Amoxicillin-Clavulanate (Augmentin) Specific Dosing
Adult Augmentin Dosing
- Standard dose: 500 mg/125 mg three times daily for mild-to-moderate infections 4
- Respiratory infections: 875 mg/125 mg twice daily for acute bacterial rhinosinusitis, community-acquired pneumonia, and acute exacerbations of chronic bronchitis 4
- Duration for uncomplicated sinusitis: 5-7 days 4