What is the recommended dosage of amoxicillin (amoxicillin) for treating strep throat?

Amoxicillin Dosage for Strep Throat

For strep throat, amoxicillin should be dosed at 50 mg/kg once daily (maximum 1000 mg) or 25 mg/kg twice daily (maximum 500 mg per dose) for children, and 500 mg twice daily for adults, always for a full 10-day course to prevent rheumatic fever. 1, 2

Pediatric Dosing

Weight-based dosing is essential for children:

• Once-daily regimen: 50 mg/kg once daily (maximum 1000 mg) for 10 days 1, 2
• Twice-daily regimen: 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days 1, 2
• Alternative dosing from FDA label: For mild/moderate infections, 25 mg/kg/day divided every 12 hours or 20 mg/kg/day divided every 8 hours 3

The once-daily formulation has been FDA-approved for patients 12 years and older and offers superior palatability and adherence compared to penicillin V suspension. 1 Research confirms that once-daily amoxicillin is non-inferior to twice-daily dosing for streptococcal pharyngitis, with bacteriologic failure rates of 20.1% versus 15.5% at 14-21 days (difference within acceptable margins). 4

Adult Dosing

Standard adult dosing:

• 500 mg twice daily for 10 days 1, 2
• Alternative: 500 mg three times daily for 10 days 1

The American Heart Association guidelines specify that adolescents and adults should receive 500 mg 2-3 times daily, with the twice-daily regimen being most commonly recommended for ease of adherence. 1

Critical Treatment Principles

The 10-day duration is non-negotiable:

• Complete the full 10-day course regardless of symptom improvement to prevent acute rheumatic fever 1, 2, 3
• Penicillin therapy effectively prevents rheumatic fever even when started up to 9 days after symptom onset 1
• Patients become non-contagious after 24 hours of antibiotic therapy, but treatment must continue for 10 days 1, 2

Administration guidance:

• Take amoxicillin at the start of a meal to minimize gastrointestinal intolerance 3
• Amoxicillin suspension is considerably more palatable than penicillin V suspension, improving adherence in children 1

Common Pitfalls to Avoid

Do NOT use shortened courses:

• While some research suggests 5-7 day courses may be effective 5, and certain cephalosporins have been studied for shorter durations 1, guidelines consistently mandate 10 days for amoxicillin or penicillin 1, 2, 3
• Meta-analyses show that 5-day penicillin courses have small but measurable clinical differences favoring 10-day treatment 1
• A 7-day penicillin regimen was superior to 3 days in resolving symptoms 1

Do NOT use amoxicillin-clavulanate (Augmentin) for uncomplicated strep throat:

• Plain amoxicillin is first-line; amoxicillin-clavulanate is reserved for chronic carriers with recurrent symptomatic episodes 2, 6
• For chronic carriers, Augmentin dosing is 40 mg/kg/day of the amoxicillin component divided into three doses for 10 days in children, or 500 mg twice daily for 10 days in adults 6

Penicillin Allergy Alternatives

For documented penicillin allergy (not amoxicillin):

• Cephalexin: 20 mg/kg/dose twice daily (maximum 500 mg/dose) for 10 days 2
• Clindamycin: 7 mg/kg/dose three times daily (maximum 300 mg/dose) for 10 days 2
• Azithromycin: 12 mg/kg once daily (maximum 500 mg) for 5 days 2
• Clarithromycin: 7.5 mg/kg/dose twice daily (maximum 250 mg/dose) for 10 days 2

Narrow-spectrum cephalosporins (cephalexin, cefadroxil) are preferred over broad-spectrum agents and should not be used in patients with immediate (anaphylactic-type) hypersensitivity to penicillin. 1 Note that 10-day clarithromycin was more effective than 5-day azithromycin in eradicating group A streptococci (91% vs 82%, p=0.012). 7

Renal Impairment Dosing

For severe renal impairment in adults and children >40 kg:

• 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
• Do NOT use 875 mg dose if GFR <30 mL/min 3

Why Amoxicillin Over Penicillin V

While penicillin V remains the traditional gold standard with proven efficacy and narrow spectrum 1, amoxicillin offers practical advantages: once-daily dosing option for patients ≥12 years, superior palatability of suspension formulations, comparable efficacy (86% vs 92% clinical cure rates), and lower cost than many alternatives. 1 Both agents have never demonstrated resistance by group A streptococci. 1