Scarlet Fever: First-Line Treatment
Penicillin or amoxicillin for 10 days is the first-line treatment for scarlet fever (the sandpaper-like rash caused by Group A Streptococcus), with penicillin V 250 mg four times daily or 500 mg twice daily for adolescents/adults, or amoxicillin 50 mg/kg once daily (maximum 1,000 mg) for children. 1, 2
Understanding Scarlet Fever
Scarlet fever is a toxin-mediated syndrome caused by Group A Streptococcus (GAS) that presents with the characteristic sandpaper-like rash alongside pharyngitis. 3 This is the same organism causing strep throat, but certain strains produce erythrogenic toxins that cause the distinctive rash.
First-Line Treatment Algorithm
For Non-Penicillin-Allergic Patients
Penicillin remains the drug of choice due to proven efficacy, safety, narrow spectrum, and low cost—with no documented penicillin resistance in GAS anywhere in the world. 1, 2
Dosing options:
- Penicillin V: 250 mg four times daily OR 500 mg twice daily for adolescents/adults for 10 days 2
- Amoxicillin: 50 mg/kg once daily (maximum 1,000 mg) OR 25 mg/kg twice daily (maximum 500 mg) for 10 days 2
- Amoxicillin is often preferred in young children due to better palatability of the suspension 1, 2
For Penicillin-Allergic Patients
First, determine the type of allergic reaction:
Non-immediate/non-anaphylactic reactions (delayed rash, mild symptoms):
- First-generation cephalosporins are safe and preferred 4, 2
- Cephalexin 20 mg/kg/dose twice daily (maximum 500 mg/dose) for 10 days 4, 2
- Cross-reactivity risk is only 0.1% in patients with non-severe, delayed penicillin reactions 4
Immediate/anaphylactic reactions (hives, angioedema, bronchospasm within 1 hour):
- Avoid ALL beta-lactams including cephalosporins due to up to 10% cross-reactivity risk 1, 4
- Clindamycin is the preferred choice: 7 mg/kg/dose three times daily (maximum 300 mg/dose) for 10 days 4, 2
- Clindamycin has approximately 1% resistance rate in the United States and is highly effective 4
- Alternative: Azithromycin 12 mg/kg once daily (maximum 500 mg) for 5 days 4, 2
- Note: Macrolide resistance is 5-8% in the United States, making clindamycin more reliable 4
Critical Treatment Duration
A full 10-day course is mandatory for all antibiotics except azithromycin to achieve maximal bacterial eradication and prevent acute rheumatic fever. 1, 2, 5 Azithromycin requires only 5 days due to its prolonged tissue half-life. 4, 2
Shortening the course by even a few days results in appreciable increases in treatment failure rates and risk of rheumatic fever. 4
Adjunctive Therapy
For symptom management:
- Acetaminophen or NSAIDs (ibuprofen) for fever and pain control 4, 6
- Avoid aspirin in children due to risk of Reye syndrome 4
- Corticosteroids are NOT recommended 4
Common Pitfalls to Avoid
Do not use these antibiotics for GAS infections:
- Trimethoprim-sulfamethoxazole (Bactrim): 50% resistance rate 4
- Tetracyclines or sulfonamides: fail to eradicate streptococci effectively 6, 2
Do not prescribe cephalosporins to patients with immediate/anaphylactic penicillin reactions—the 10% cross-reactivity risk is too high. 1, 4
Do not shorten treatment duration below 10 days (except azithromycin's 5-day course)—this increases treatment failure and complication risk. 4, 2
When Invasive Disease is Suspected
If scarlet fever progresses to streptococcal toxic shock syndrome or necrotizing fasciitis (severe toxin-mediated syndromes), combination therapy with clindamycin PLUS penicillin is essential. 1 Clindamycin suppresses streptococcal toxin and cytokine production and was found superior to penicillin alone in animal models and observational studies. 1 These severe presentations require immediate hospitalization and surgical consultation.
Follow-Up Considerations
Routine post-treatment throat cultures are not recommended for asymptomatic patients who have completed therapy. 1 Testing should only be considered in special circumstances, such as patients with a history of rheumatic fever. 4