Antibiotics of Choice for Strep A in Adults
Penicillin remains the first-line treatment for Group A streptococcal infections in adults due to its proven efficacy, safety, narrow spectrum, and low cost. 1
First-Line Treatment Options
- Oral penicillin V is recommended for adults at 250 mg three to four times daily or 500 mg twice daily for 10 days 1
- Amoxicillin can be used as an alternative to penicillin V with equal efficacy 1
- For patients unlikely to complete a full 10-day course of oral therapy, intramuscular benzathine penicillin G (1.2 million units as a single dose) is preferred 1
Treatment for Penicillin-Allergic Patients
- For non-immediate penicillin allergy, first-generation cephalosporins (such as cephalexin) can be used 2
- For patients with immediate hypersensitivity to penicillin, erythromycin is a suitable alternative 1
- Clindamycin (7 mg/kg per dose three times daily, maximum 300 mg per dose, for 10 days) is recommended for patients with severe penicillin allergy 2
Treatment Duration Considerations
- Most oral antibiotics must be administered for a full 10-day course to achieve maximal pharyngeal eradication of Group A streptococci 1
- Azithromycin is an exception, requiring only a 5-day course (500 mg on day 1, followed by 250 mg once daily for 4 days) due to its prolonged tissue half-life 1, 3
Special Considerations for Invasive Infections
- For invasive Group A streptococcal infections (like bacteremia), a combination of intravenous penicillin G plus clindamycin is recommended 4
- Clindamycin suppresses streptococcal toxin production while penicillin provides bactericidal activity 4, 5
Common Pitfalls and Caveats
- Sulfonamides and tetracyclines should not be used for treatment of Group A streptococcal pharyngitis due to higher rates of resistance 1
- Macrolide resistance among Group A streptococci varies geographically, with rates around 5-8% in the United States 2
- Penicillin alone may be inadequate for severe invasive Group A streptococcal infections due to the "Eagle effect" (large inoculum effect) 4, 5
- Although some studies suggest that first-generation cephalosporins may have better eradication rates than penicillin, current guidelines still recommend penicillin as first-line therapy due to its long track record of safety and efficacy 6
- Twice-daily dosing of penicillin V (500 mg) has been shown to be as effective as three-times-daily dosing (250 mg), which may improve adherence 7
Management of Close Contacts and Carriers
- It is usually not necessary to perform throat cultures for asymptomatic household contacts of patients with Group A streptococcal pharyngitis 1
- For documented outbreaks in group settings (schools, day care centers), throat cultures should be performed for all patients, but only those with positive cultures should receive antimicrobial treatment 1
- Clindamycin has demonstrated high efficacy in eradicating streptococci in chronic carriers 2