What is the recommended dosage of amoxicillin (bid vs tid) for a patient with strep throat, considering factors such as age, weight, medical history, and history of antibiotic allergies or sensitivities?

Amoxicillin for Strep Throat: BID Dosing is Equally Effective and Preferred

For strep throat, amoxicillin 500 mg twice daily (BID) for 10 days is the recommended regimen for adolescents and adults, while children should receive 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days. 1, 2

Why BID Dosing is Preferred Over TID

The IDSA guidelines explicitly endorse both once-daily and twice-daily amoxicillin dosing with "Strong, high" quality evidence, making BID the practical choice for most patients 1, 2:

• Adolescents and adults: 500 mg twice daily for 10 days 1
• Children: 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days 1, 2
• Alternative once-daily option: 50 mg/kg once daily (maximum 1,000 mg) for 10 days 1, 2

The BID regimen offers superior adherence compared to TID or QID dosing while maintaining equivalent bacteriologic eradication rates 2. Amoxicillin suspension is considerably more palatable than penicillin V, particularly important for pediatric patients 1.

Critical Treatment Requirements

All patients must complete the full 10-day course to prevent acute rheumatic fever, even when symptoms resolve after 2-3 days 1. This is non-negotiable—shortening the course by even a few days dramatically increases treatment failure rates and rheumatic fever risk 3.

The 10-day duration is required because:

• Prevents acute rheumatic fever (can be started up to 9 days after symptom onset and still prevent this complication) 1
• Achieves maximal pharyngeal eradication of Group A Streptococcus 3
• Reduces suppurative complications 3
• Patients become non-contagious after 24 hours of therapy 1

Evidence Supporting BID vs TID Dosing

Research demonstrates that higher-dose amoxicillin (40 mg/kg/day) achieves superior bacteriologic cure rates (79.3%) compared to standard-dose penicillin V (54.5%, P=0.005), with clinical cure rates of 87.9% vs 70.9% (P=0.025) 4. The current perception that penicillin is declining in effectiveness may actually reflect inadequate dosing rather than true resistance 4.

Penicillin resistance has never been documented anywhere in the world, making amoxicillin's advantage primarily related to improved palatability, adherence, and pharmacokinetics rather than antimicrobial superiority 1, 3.

Alternatives for Penicillin-Allergic Patients

Non-Immediate (Non-Anaphylactic) Penicillin Allergy

First-generation cephalosporins are preferred with only 0.1% cross-reactivity risk 3:

• Cephalexin: 500 mg twice daily for 10 days (adults) or 20 mg/kg twice daily (children, maximum 500 mg/dose) 1, 3
• Cefadroxil: 30 mg/kg once daily (maximum 1 gram) for 10 days 1, 3

Immediate/Anaphylactic Penicillin Allergy

Avoid all beta-lactams due to 10% cross-reactivity risk 1, 3. Use:

• Clindamycin (preferred): 300 mg three times daily for 10 days (adults) or 7 mg/kg three times daily (children, maximum 300 mg/dose) 1, 3. Resistance is only ~1% in the US 3
• Azithromycin: 500 mg once daily for 5 days (adults) or 12 mg/kg once daily (children, maximum 500 mg) 1, 3. Note: 5-8% macrolide resistance in the US 3
• Clarithromycin: 250 mg twice daily for 10 days (adults) or 7.5 mg/kg twice daily (children, maximum 250 mg/dose) 1, 3

Common Pitfalls to Avoid

1. Never prescribe less than 10 days (except azithromycin's 5-day course)—this increases treatment failure and rheumatic fever risk 3
2. Never use cephalosporins in patients with immediate/anaphylactic penicillin reactions—10% cross-reactivity can cause life-threatening reactions 1, 3
3. Never use trimethoprim-sulfamethoxazole (Bactrim)—50% resistance rates make it ineffective for Group A Streptococcus 3
4. Don't assume all penicillin-allergic patients need non-beta-lactams—only those with immediate/anaphylactic reactions must avoid cephalosporins 3
5. Don't prescribe broad-spectrum cephalosporins when narrow-spectrum first-generation agents work—this unnecessarily selects for resistant flora 1

Administration Tips

Take amoxicillin at the start of meals to minimize gastrointestinal intolerance 5. After reconstitution, amoxicillin suspension must be discarded after 14 days; refrigeration is preferable but not required 5. Shake suspension well before each use 5.

When to Reevaluate

Patients with worsening symptoms after appropriate antibiotic initiation or symptoms lasting 5 days after starting treatment require reevaluation 6. However, routine post-treatment throat cultures are not recommended for asymptomatic patients who completed therapy 3.