What is the recommended dosage of amoxicillin (amoxicillin) for a child or adult with strep throat and no known allergies to penicillin (penicillin)?

Amoxicillin Dosing for Strep Throat

For adults with strep throat and no penicillin allergy, prescribe amoxicillin 500 mg orally twice daily for 10 full days; for children, prescribe 50 mg/kg once daily (maximum 1000 mg) or 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days. 1, 2

Adult Dosing

• The standard adult dose is amoxicillin 500 mg orally twice daily for 10 days, which is equivalent to the weight-based pediatric dosing when scaled appropriately 1
• The FDA label confirms this dosing for ear/nose/throat infections including streptococcal pharyngitis, with 500 mg every 12 hours for mild to moderate infections 2
• The full 10-day course must be completed regardless of symptom improvement to prevent acute rheumatic fever, even though patients become non-contagious after just 24 hours of therapy 1, 2

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

• The Infectious Diseases Society of America recommends amoxicillin 50 mg/kg once daily (maximum 1000 mg) for 10 days as the preferred regimen, with strong, high-quality evidence supporting this approach 3, 1
• An alternative regimen is 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days, which demonstrates equivalent efficacy 3, 1
• Both once-daily and twice-daily regimens are superior to penicillin V and have better compliance rates 3
• For severe infections, the FDA label supports higher dosing of 45 mg/kg/day divided every 12 hours or 40 mg/kg/day divided every 8 hours 2

Why Amoxicillin Over Penicillin V

• Amoxicillin at 40-50 mg/kg/day achieves significantly better clinical cure (87.9% vs 70.9%) and bacteriologic cure (79.3% vs 54.5%) compared to standard-dose penicillin V 4
• The carrier rate is also lower with amoxicillin (10.3%) compared to penicillin V (23.6%) 4
• Amoxicillin has superior middle ear fluid penetration and better oral absorption than penicillin V 3

Critical Administration Details

• Administer amoxicillin at the start of a meal to minimize gastrointestinal intolerance 2
• For oral suspension, shake well before each use and discard any unused portion after 14 days 2
• Refrigeration of suspension is preferable but not required 2

Treatment Duration: Non-Negotiable

• All patients must complete the full 10-day course to achieve maximal pharyngeal eradication of Group A Streptococcus and prevent acute rheumatic fever, regardless of symptom resolution 3, 1, 2
• Treatment should continue for a minimum of 48-72 hours beyond when the patient becomes asymptomatic 2
• Even though a single dose of amoxicillin (50 mg/kg) results in non-detection of Group A Streptococcus in 91% of children by the next morning, the full 10-day course remains essential for preventing complications 5

When NOT to Use Standard Amoxicillin

• Do not use amoxicillin in patients with documented penicillin allergy - see alternative regimens below 6
• Reserve amoxicillin-clavulanate (Augmentin) for treatment failures or chronic Group A Streptococcus carriers who have failed first-line therapy, not for initial treatment 3
• For Augmentin when indicated, dose at 40 mg/kg/day of the amoxicillin component divided into three doses (maximum 2000 mg/day) for 10 days 3

Alternative Antibiotics for Penicillin Allergy

For Non-Immediate (Non-Anaphylactic) Penicillin Allergy:

• First-generation cephalosporins are the preferred first-line alternatives with strong, high-quality evidence 6
• Cephalexin 500 mg orally twice daily for 10 days (adults) or 20 mg/kg/dose twice daily (maximum 500 mg/dose) for 10 days (children) 6, 1
• Cefadroxil 30 mg/kg once daily (maximum 1 gram) for 10 days (children) 6, 1
• Cross-reactivity risk is only 0.1% in patients with non-severe, delayed penicillin reactions 6

For Immediate/Anaphylactic Penicillin Allergy:

• Clindamycin is the preferred choice with only 1% resistance among Group A Streptococcus in the United States 6
• Clindamycin 300 mg orally three times daily for 10 days (adults) or 7 mg/kg/dose three times daily (maximum 300 mg/dose) for 10 days (children) 6, 1
• Azithromycin 500 mg once daily for 5 days (adults) or 12 mg/kg once daily (maximum 500 mg) for 5 days (children) is acceptable but has 5-8% macrolide resistance 6, 1
• Clarithromycin 250 mg twice daily for 10 days (adults) or 7.5 mg/kg/dose twice daily (maximum 250 mg/dose) for 10 days (children) 6, 1

Common Pitfalls to Avoid

• Do not prescribe courses shorter than 10 days (except azithromycin's 5-day regimen) - this dramatically increases treatment failure rates and risk of acute rheumatic fever 6
• Do not use cephalosporins in patients with immediate/anaphylactic penicillin reactions - up to 10% cross-reactivity risk exists with all beta-lactams 6
• Do not use amoxicillin-clavulanate as first-line therapy - plain amoxicillin is appropriate for uncomplicated streptococcal pharyngitis 3
• Do not assume all penicillin-allergic patients need macrolides - first-generation cephalosporins are safe for non-immediate reactions 6

Special Considerations

• For patients with severe renal impairment (GFR <30 mL/min), reduce dosing to 500 mg or 250 mg every 12 hours; for GFR <10 mL/min, reduce to every 24 hours 2
• Patients with GFR <30 mL/min should NOT receive the 875 mg dose 2
• For hemodialysis patients, administer an additional dose both during and at the end of dialysis 2
• When compliance cannot be assured, consider benzathine penicillin G as a single intramuscular injection: 600,000 units for children <27 kg or 1,200,000 units for children ≥27 kg and adults 3