Treatment of Infections Caused by Gram-Positive Cocci in Chains (Streptococcus Species)
For Streptococcus species infections, penicillin remains the first-line treatment due to its proven efficacy, narrow spectrum, and lack of documented resistance, with specific regimens determined by the type of infection and penicillin susceptibility of the isolate. 1
Treatment Based on Streptococcal Species and Susceptibility
Penicillin-Susceptible Streptococci (MIC ≤0.12 μg/mL)
- First-line therapy: Penicillin V or amoxicillin for 10 days 1, 2
- Penicillin V: 250-500 mg orally every 6-8 hours for adults
- Amoxicillin: 50 mg/kg once daily (maximum 1000 mg) or 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days
- For penicillin-allergic patients: Clindamycin or macrolides (e.g., azithromycin) 1
- Azithromycin: 12 mg/kg once daily (max 500 mg) for 5 days
- Clindamycin: 300-450 mg orally three times daily for 10 days
Penicillin-Resistant Streptococci (MIC >0.12 μg/mL)
- Relatively resistant (MIC 0.12-0.5 μg/mL):
- Penicillin or ceftriaxone plus gentamicin for 2 weeks 3
- Penicillin: 24 million units/day IV in 4-6 divided doses for 4 weeks
- Gentamicin: 3 mg/kg/day IV or IM in 1 dose for 2 weeks
- Fully resistant (MIC >0.5 μg/mL):
Treatment by Specific Clinical Scenarios
Streptococcal Pharyngitis (Strep Throat)
- Standard regimen: Penicillin V or amoxicillin for 10 days 1, 4
- Critical to complete full 10-day course to prevent rheumatic fever
- Return to work/school: After 24 hours of appropriate antibiotic therapy 1
Invasive Streptococcal Infections (Necrotizing Fasciitis/Toxic Shock Syndrome)
- Recommended regimen: Clindamycin plus penicillin (A-II) 3
- Rationale: Clindamycin suppresses toxin production and modulates cytokine production
- Penicillin should be added due to increasing resistance of Group A strep to macrolides
Streptococcal Endocarditis
- Native valve endocarditis: 3
- Penicillin G: 24 million units/day IV in 4-6 divided doses for 4 weeks
- Plus gentamicin: 3 mg/kg/day IV or IM in 1 dose for first 2 weeks
- Prosthetic valve endocarditis: Extended therapy for 6 weeks 3
Abiotrophia/Granulicatella Species (Nutritionally Variant Streptococci)
- Treat with regimens recommended for enterococcal endocarditis 3
- Combination of ampicillin or penicillin plus gentamicin for 6 weeks
Special Considerations
Pediatric Patients
- Dosing adjustments required based on age and weight 3, 2
- For children <12 weeks: Maximum dose of 30 mg/kg/day of amoxicillin divided every 12 hours 2
Penicillin-Allergic Patients
- Alternative options: 3
- Vancomycin: 30 mg/kg/day IV in 2 doses
- Clindamycin: 600-900 mg/kg every 8 hours IV
- Azithromycin: For less severe infections
Patients with Renal Impairment
- Dose adjustment required for GFR <30 mL/min 2
- Patients on hemodialysis require additional doses during and after dialysis
Monitoring and Duration
- Continue treatment for 48-72 hours beyond symptom resolution 3
- For streptococcal pharyngitis: Minimum 10 days to prevent rheumatic fever 2, 4
- For endocarditis: 4-6 weeks depending on valve involvement 3
Common Pitfalls to Avoid
- Inadequate duration: Failing to complete the full course (especially the 10-day requirement for strep throat)
- Inappropriate empiric therapy: Using broad-spectrum antibiotics when narrow-spectrum would suffice
- Missing resistant strains: Not considering penicillin resistance in treatment failures
- Overlooking toxin-mediated disease: Not adding clindamycin for invasive streptococcal infections
Despite increasing antibiotic resistance globally, streptococci have maintained relatively good susceptibility to penicillin compared to other bacterial groups 5. However, clinicians should be aware of the rising incidence of penicillin-resistant strains, particularly among viridans group streptococci, which may necessitate alternative treatment approaches 3.