What is the recommended treatment for strep D (Streptococcus group D) infections?

Treatment of Group D Streptococcal Infections

For Group D streptococcal infections, the recommended treatment is a combination of penicillin or ampicillin with an aminoglycoside (such as gentamicin) for synergistic bactericidal activity, particularly in serious infections like endocarditis. 1, 2

First-Line Treatment Options

For Serious Infections (Endocarditis, Bacteremia):

• Penicillin G or Ampicillin plus Gentamicin
  • Ampicillin: 12 g/day IV in 4-6 divided doses 1
  • Gentamicin: 3 mg/kg/day IV or IM in 2-3 divided doses 1
  • Duration: 4-6 weeks for native valve endocarditis, minimum 6 weeks for prosthetic valve endocarditis 1, 2

For Less Severe Infections:

• Ampicillin (oral)

  • 500 mg four times daily for gastrointestinal or genitourinary tract infections 3
  • 250 mg four times daily for respiratory tract infections 3
  • Duration: Minimum 48-72 hours after patient becomes asymptomatic 3

• Penicillin V (oral)

  • 500 mg four times daily for 10 days 2

Alternative Regimens for Penicillin-Allergic Patients

• Vancomycin

  • 30 mg/kg/day IV in 2 doses for 4-6 weeks 1, 2
  • Serum levels should be monitored: pre-dose (trough) 10-15 mg/L, post-dose (peak) 30-45 mg/L 1

• Clindamycin

  • 300 mg four times daily for 10 days 1, 2

• Azithromycin

  • 500 mg once daily for 5 days 1, 2

Important Clinical Considerations

Monitoring During Treatment

• When using gentamicin, monitor renal function and serum gentamicin concentrations weekly 1
  • Pre-dose (trough) concentrations should be <1 mg/L
  • Post-dose (peak) concentrations should be 10-12 mg/L

Resistance Patterns

• Group D streptococci, particularly enterococci, are relatively resistant to penicillins compared to other streptococci 4, 5
• High-level resistance to aminoglycosides has been reported in some enterococcal strains (up to 40% for Enterococcus faecalis) 5
• Streptococcus bovis (a non-enterococcal Group D streptococcus) is generally more susceptible to antibiotics than enterococci 6

Treatment Challenges

• Combination therapy with penicillin/ampicillin plus an aminoglycoside is essential for treating serious Group D streptococcal infections due to their relative resistance 4, 7
• For strains with high-level aminoglycoside resistance, alternative regimens may be necessary, and surgical intervention might be required in cases of endocarditis 7

Treatment Duration

• Minimum 48-72 hours after patient becomes asymptomatic 3, 8
• For endocarditis: 4-6 weeks for native valve, minimum 6 weeks for prosthetic valve 1, 2
• For infections caused by hemolytic strains of streptococci, minimum 10 days to prevent rheumatic fever or glomerulonephritis 3

Common Pitfalls to Avoid

1. Monotherapy failure: Group D streptococci, especially enterococci, often require combination therapy for serious infections 4, 7
2. Inadequate duration: Shorter courses may lead to treatment failure and complications 1, 3
3. Failure to monitor aminoglycoside levels: Can lead to toxicity or subtherapeutic levels 1
4. Not distinguishing between enterococcal and non-enterococcal Group D streptococci: Streptococcus bovis is more susceptible to antibiotics than enterococci 6
5. Overlooking resistance patterns: Some strains may have high-level resistance to aminoglycosides, requiring alternative approaches 5, 7

Remember that treatment success depends on proper identification of the specific Group D streptococcal species, appropriate antibiotic selection based on susceptibility testing, and adequate duration of therapy.