What is the antibiotic of choice for a patient with a positive Anti-Streptolysin O (ASLO) test and ankle joint swelling, suggestive of acute rheumatic fever?

Antibiotic of Choice for ASLO-Positive Ankle Joint Swelling

Penicillin is the definitive antibiotic of choice for treating group A streptococcal infection in a patient with positive ASLO and ankle joint swelling suggestive of acute rheumatic fever. 1, 2

Primary Treatment Regimen

Benzathine penicillin G is the preferred formulation because it ensures complete treatment adherence and has proven efficacy in preventing rheumatic fever progression. 1, 2

Dosing for Primary Treatment:

• Intramuscular benzathine penicillin G: Single injection of 600,000 units for patients <27 kg (60 lb); 1,200,000 units for patients ≥27 kg 1, 2, 3
• Oral penicillin V alternative: 250 mg 2-3 times daily for 10 days (children <27 kg); 500 mg 2-3 times daily for 10 days (≥27 kg, adolescents, adults) 1, 2

Why Penicillin is Superior:

• Only antibiotic proven in controlled trials to prevent initial attacks of rheumatic fever 1, 2
• No documented resistance worldwide - group A streptococci have never developed penicillin resistance 1, 2
• Cost-effective with narrow spectrum of activity 1
• Warming benzathine penicillin G to room temperature before injection reduces discomfort 3

Alternative Regimens for Penicillin Allergy

For documented penicillin allergy, acceptable alternatives include: 1, 4

• Narrow-spectrum cephalosporin (e.g., cephalexin): Variable dosing for 10 days - avoid in patients with immediate (type I) hypersensitivity 1
• Clindamycin: 20 mg/kg/day divided in 3 doses (maximum 1.8 g/day) for 10 days 1
• Azithromycin: 12 mg/kg once daily (maximum 500 mg) for 5 days 1
• Clarithromycin: 15 mg/kg/day divided twice daily (maximum 250 mg twice daily) for 10 days 1
• Erythromycin: Acceptable alternative with <5% resistance rates in the United States 1, 2, 4

Critical Secondary Prevention

Immediately initiate continuous antimicrobial prophylaxis after treating the acute infection to prevent recurrent attacks, which carry extremely high risk in patients who have had rheumatic fever. 1, 3

Secondary Prophylaxis Regimen:

• Benzathine penicillin G: 1,200,000 units intramuscularly every 4 weeks (or every 3 weeks in high-risk situations) 2, 3
• Duration depends on cardiac involvement: at least 10 years or until age 40 (whichever is longer) for those with persistent valvular disease 3

Important Clinical Considerations

Treatment timing is flexible - penicillin can be started up to 9 days after symptom onset and still effectively prevent rheumatic fever progression. 2, 3

Patients become non-contagious after 24 hours of antibiotic therapy. 2, 3

Complete the full 10-day course even if throat culture is negative at diagnosis, as this eradicates residual group A streptococcus. 3

Common Pitfalls to Avoid

Do not use sulfonamides, tetracyclines, or fluoroquinolones - these are not acceptable for treating streptococcal pharyngitis due to resistance patterns and failure to eradicate organisms. 1

Avoid broad-spectrum cephalosporins when narrow-spectrum agents are appropriate, as they are more expensive and select for resistant flora. 3

Intramuscular benzathine penicillin G should be strongly considered for patients with personal or family history of rheumatic fever, those unlikely to complete oral therapy, or those with environmental risk factors. 3