What is the recommended treatment for Group G Streptococcus infections?

Treatment of Group G Streptococcus Infections

Penicillin remains the first-line treatment for Group G Streptococcus infections, with all isolates demonstrating universal susceptibility to penicillin, ampicillin, cephalosporins, clindamycin, and vancomycin. 1, 2

First-Line Antibiotic Therapy

Group G Streptococcus infections should be treated with penicillin-based regimens, mirroring the approach used for Group A Streptococcus:

For Patients Without Penicillin Allergy

• Penicillin V (oral): 250-500 mg four times daily or 500 mg twice daily for adults; 250 mg two to three times daily for children 3
• Amoxicillin (oral): 500 mg three times daily for adults; 50 mg/kg once daily (maximum 1,000 mg) or 25 mg/kg twice daily (maximum 500 mg) for children 3, 4
• Penicillin G benzathine (intramuscular): Single dose of 600,000 units for patients <27 kg or 1,200,000 units for patients ≥27 kg 3, 5
• Penicillin G (intravenous): For severe invasive infections including endocarditis (12-20 million units/day), meningitis (24 million units/day as 2 million units every 2 hours), or bacteremia 6, 7

For Patients With Penicillin Allergy

• First-generation cephalosporins (avoid in anaphylactic-type allergy): Cephalexin 20 mg/kg twice daily (maximum 500 mg per dose) or cefadroxil 30 mg/kg once daily (maximum 1 g) for 10 days 3, 8
• Clindamycin: 7 mg/kg three times daily (maximum 300 mg per dose) for 10 days; all Group G isolates are susceptible 3, 2
• Vancomycin: Reserved for severe infections or true penicillin allergy; all isolates are susceptible 2

Treatment Duration

• Standard infections: 10 days minimum to ensure complete eradication and prevent complications 3, 4
• Endocarditis: 4-6 weeks of intravenous therapy 6, 2, 7
• Meningitis: 10-14 days of high-dose intravenous penicillin 6
• Septic arthritis/osteomyelitis: Extended therapy based on clinical response 2
• Continue treatment for at least 48-72 hours beyond resolution of symptoms 3, 6

Clinical Considerations Specific to Group G Streptococcus

Infection Characteristics

Group G Streptococcus typically affects patients with underlying conditions including diabetes (24.3%), cardiovascular disease (21.6%), malignancy (21.6%), bone/joint disease (18.9%), and cirrhosis (13.5%) 2. The most common portal of entry is skin (64.9%), leading to:

• Cellulitis (32.4%) 2
• Primary bacteremia (27%) 2
• Septic arthritis or osteomyelitis (16.2%) 2
• Endocarditis (8.1%), including cases without pre-existing valvular disease 2, 7
• Meningitis (8.1%) 2
• Streptococcal toxic shock syndrome (rare but documented) 9

Important Clinical Pitfalls

Inoculum effect: Group G Streptococcus demonstrates an inoculum effect where high bacterial loads significantly reduce the rate of penicillin-mediated killing (5-6 times slower), which may explain therapeutic failures or relapses despite antibiotic susceptibility 1. This finding suggests:

• Source control (drainage of abscesses, debridement of infected tissue) is critical 2
• Poor response to appropriate antibiotics should prompt investigation for undrained foci rather than antibiotic resistance 2
• Higher penicillin doses may be needed for high-burden infections 1

Rapid clinical improvement expected: Group G Streptococcus is considered a low-virulence organism with typically fast clinical improvement after appropriate therapy 2. Lack of improvement within 48-72 hours warrants:

• Reassessment for undrained infection sites 2
• Evaluation of underlying diseases that may impair response 2
• Consideration of complications such as endocarditis or deep-seated infection 2, 7

Adjunctive Therapy

• Analgesics/antipyretics: Acetaminophen or NSAIDs for moderate to severe symptoms or fever control 3, 5
• Avoid aspirin in children due to Reye syndrome risk 3
• Intravenous immunoglobulin: Consider for streptococcal toxic shock syndrome caused by Group G Streptococcus, based on successful case series 9
• Surgical intervention: Debridement or drainage as indicated for necrotizing infections or abscesses 6, 2

Antimicrobial Susceptibility Profile

All Group G Streptococcus isolates studied demonstrate susceptibility to penicillin (MIC90 0.03 mcg/mL), ampicillin (MIC90 ≤0.015 mcg/mL), oxacillin, cefazolin, clindamycin, and vancomycin 1, 2. Tolerance has not been demonstrated using standard testing methods 1.