What is the recommended IV treatment for group B streptococcus (GBS) infections?

IV Treatment for Group B Streptococcus Infections

Penicillin G remains the first-line IV treatment for GBS infections, with an initial dose of 5 million units IV followed by 2.5-3.0 million units every 4 hours, or alternatively ampicillin 2 g IV initial dose then 1 g every 4 hours. 1

First-Line Treatment Options

For patients without penicillin allergy:

• Penicillin G: 5 million units IV loading dose, then 2.5-3.0 million units IV every 4 hours until delivery 1
• Ampicillin: 2 g IV loading dose, then 1 g IV every 4 hours until delivery 1
• All GBS isolates remain universally susceptible to penicillin, ampicillin, cefazolin, cefotaxime, and vancomycin 2

The choice between penicillin G and ampicillin is largely institutional preference, as both achieve excellent intraamniotic concentrations and maintain universal GBS susceptibility 1, 2.

Penicillin-Allergic Patients: Risk Stratification Required

The critical decision point is determining allergy severity:

Low-Risk Penicillin Allergy (No history of anaphylaxis, angioedema, respiratory distress, or urticaria)

• Cefazolin: 2 g IV loading dose, then 1 g IV every 8 hours until delivery 1, 3
• Cefazolin is preferred because pharmacologic data demonstrate effective intraamniotic concentrations 3
• Approximately 10% cross-reactivity risk exists between penicillin and cephalosporins 3

High-Risk Penicillin Allergy (History of anaphylaxis, angioedema, respiratory distress, or urticaria)

The treatment depends on GBS susceptibility testing:

• If GBS isolate is susceptible to both clindamycin AND erythromycin: Clindamycin 900 mg IV every 8 hours until delivery 1, 3
• If susceptibility unknown or isolate resistant: Vancomycin 1 g IV every 12 hours until delivery 1, 3

Critical caveat: Resistance to erythromycin often indicates inducible clindamycin resistance, even if the isolate appears susceptible to clindamycin 1. If an isolate is erythromycin-resistant but clindamycin-susceptible, testing for inducible resistance must be performed before using clindamycin 1.

Rising Resistance Patterns: Clinical Implications

Resistance trends are concerning for second-line agents:

• Clindamycin resistance increased from 10.5% to 15.0% over surveillance periods 2
• Erythromycin resistance increased from 15.8% to 32.8%, now affecting 25.6% of isolates 2
• Resistance is particularly associated with serotype V 2
• Erythromycin (21% resistance) is inferior to clindamycin (4% resistance) as an alternative agent 4

These data underscore why vancomycin becomes necessary when susceptibility testing is unavailable in high-risk allergy patients 1, 3.

Treatment for Invasive GBS Disease

For serious infections beyond intrapartum prophylaxis:

• Penicillin G 5-24 million units/day in divided doses every 4-6 hours, depending on infection severity 5
• For meningitis: 12-24 million units/day as 2-4 million units every 4 hours for 10-14 days 5
• For endocarditis: 12-20 million units/day for 4-6 weeks 5

Special Considerations for Chorioamnionitis

Broader spectrum coverage may be necessary:

• Standard GBS prophylaxis regimens may be insufficient 1, 6
• Broader spectrum agents active against GBS and other organisms (including E. coli and gram-negative pathogens) should be considered 1
• Consultation with obstetric providers is essential as chorioamnionitis signs can be nonspecific 6

Common Pitfalls to Avoid

Dosing errors with cefazolin:

• The 2 g loading dose is essential for rapid therapeutic levels—do not underdose 3
• The 8-hour dosing interval is longer than typical cefazolin dosing due to pregnancy-related pharmacokinetic changes 3

Allergy history verification:

• Many reported penicillin allergies are not true IgE-mediated reactions 3
• Detailed allergy history can identify patients who can safely receive penicillin rather than alternatives 3

Timing of prophylaxis:

• Intrapartum antibiotic prophylaxis is effective within 2-4 hours of administration 1
• At least 4 hours of IV antibiotics before delivery is required for adequate neonatal protection 1

Resistance testing:

• When clindamycin is considered for high-risk allergy patients, both clindamycin AND erythromycin susceptibility must be confirmed 1, 3
• If testing is unavailable at labor onset, default to vancomycin for high-risk allergy patients 1