Amoxicillin Dosing for Strep Pharyngitis
For strep-positive pharyngitis, use amoxicillin 1000 mg once daily OR 500 mg twice daily for 10 days in adults, and 50 mg/kg once daily (maximum 1000 mg) OR 25 mg/kg twice daily (maximum 500 mg per dose) in children. 1, 2, 3
Adult Dosing Recommendations
Standard amoxicillin (not Augmentin) is the first-line treatment for Group A streptococcal pharyngitis due to its narrow spectrum, minimal adverse effects, and low cost. 1
Preferred Regimens for Adults:
- Once-daily dosing: 1000 mg once daily for 10 days 1
- Twice-daily dosing: 500 mg twice daily for 10 days 1, 3
The 10-day duration is mandatory to prevent acute rheumatic fever, regardless of clinical improvement. 1, 3
Pediatric Dosing Recommendations
Standard Dosing for Children:
- Once-daily: 50 mg/kg once daily (maximum 1000 mg) for 10 days 2, 3, 4
- Twice-daily: 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days 2, 3
Once-daily amoxicillin is non-inferior to twice-daily dosing for strep pharyngitis, with bacteriologic failure rates of 20.1% vs 15.5% at 14-21 days, and 2.8% vs 7.1% at 28-35 days respectively. 4
Higher-Dose Option:
For treatment failures or suspected resistant organisms, 40 mg/kg/day divided twice daily can be used, which shows superior clinical cure (87.9% vs 70.9%) and bacteriologic cure (79.3% vs 54.5%) compared to standard-dose penicillin V. 5
When to Use Augmentin (Amoxicillin-Clavulanate) Instead
Augmentin is NOT first-line for acute strep pharyngitis. 1 It should be reserved for specific situations:
Chronic Streptococcal Carriers:
- Adults: 500 mg (amoxicillin component) twice daily for 10 days 1
- Children: 40 mg/kg/day of amoxicillin component divided into three doses (maximum 2000 mg/day) for 10 days 1, 2
The addition of clavulanate helps eradicate streptococci that are more difficult to eliminate from the pharynx in chronic carriers with recurrent symptomatic episodes. 1
Dosing Frequency Evidence
Twice-daily dosing is as efficacious as three or four times daily dosing for penicillin/amoxicillin in strep pharyngitis. 6 However, once-daily penicillin (not amoxicillin) shows 12 percentage points lower cure rates and should not be used. 6
Special Populations
Renal Impairment:
- 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
Infants <3 Months:
Maximum dose is 30 mg/kg/day divided every 12 hours due to incompletely developed renal function. 3
Critical Implementation Points
Mandatory 10-Day Duration:
All streptococcal infections require a minimum 10-day course to prevent acute rheumatic fever, regardless of clinical improvement. 1, 3 This is non-negotiable even if the patient becomes asymptomatic earlier.
Administration Timing:
Take at the start of a meal to minimize gastrointestinal intolerance. 3
Common Pitfalls to Avoid:
- Do not use Augmentin as first-line therapy for acute strep pharyngitis—plain amoxicillin is preferred. 1
- Do not substitute two 250 mg tablets for one 500 mg tablet of Augmentin, as this results in excessive clavulanate dosing. 1
- Do not use once-daily penicillin (as opposed to amoxicillin), which has inferior efficacy. 6
- Do not stop treatment early even if symptoms resolve—complete the full 10 days. 1, 3
Penicillin-Allergic Patients:
Use cephalexin, clindamycin, azithromycin, or clarithromycin instead of amoxicillin or Augmentin. 1