What is the choice of antibiotic for Group B Streptococcus (GBS) in pregnancy?

Antibiotic Choice for Group B Streptococcus (GBS) in Pregnancy

For Group B Streptococcus in pregnancy, intravenous penicillin G (5 million units IV initial dose, then 2.5-3.0 million units IV every 4 hours until delivery) is the first-line antibiotic of choice, with ampicillin as an acceptable alternative. 1, 2

First-Line Treatment Options

For non-penicillin allergic patients:

• Penicillin G: 5 million units IV initial dose, then 2.5-3.0 million units IV every 4 hours until delivery 1, 2
• Ampicillin: 2 g IV initial dose, then 1 g IV every 4 hours until delivery (alternative) 1, 2

Management Algorithm for Penicillin-Allergic Patients

For patients with penicillin allergy, treatment depends on the risk of anaphylaxis:

Low Risk for Anaphylaxis (no history of anaphylaxis, angioedema, respiratory distress, or urticaria):

• Cefazolin: 2 g IV initial dose, then 1 g IV every 8 hours until delivery 1, 2

High Risk for Anaphylaxis:

1. If GBS isolate is tested and susceptible to clindamycin and erythromycin:

   • Clindamycin: 900 mg IV every 8 hours until delivery 1

2. If GBS isolate is resistant to erythromycin but susceptible to clindamycin:

   • Clindamycin can be used if testing for inducible clindamycin resistance is negative 1

3. If GBS isolate is resistant to clindamycin, shows inducible resistance, or susceptibility is unknown:

   • Vancomycin: 1 g IV every 12 hours until delivery 1, 2

Important Clinical Considerations

• Susceptibility testing is essential for penicillin-allergic patients due to increasing resistance to alternative antibiotics 2
• Erythromycin is no longer recommended for GBS prophylaxis due to increasing resistance and poor placental transfer 2
• Intrapartum antibiotics should ideally be administered at least 4 hours before delivery for maximum effectiveness 1, 2, 3
• Oral antibiotics during pregnancy are not effective for eliminating GBS colonization or preventing neonatal disease 2

Indications for Intrapartum Antibiotic Prophylaxis

Antibiotics should be administered to women with:

• Positive GBS vaginal-rectal screening culture in current pregnancy
• GBS bacteriuria during any trimester of current pregnancy
• Previous infant with invasive GBS disease
• Unknown GBS status at labor onset with risk factors (preterm delivery, rupture of membranes >18 hours, or intrapartum fever) 2, 4

Potential Pitfalls and Caveats

• Failure to perform susceptibility testing in penicillin-allergic patients may lead to inappropriate antibiotic selection and treatment failure 2
• Administering antibiotics less than 4 hours before delivery reduces effectiveness, though antibiotics should still be initiated as soon as possible 2, 3
• The risk of anaphylaxis with penicillin is estimated at about 5 cases per 10,000 treatments, which can have severe consequences for both mother and child 5
• Treating GBS colonization with oral antibiotics in the third trimester is ineffective, as 30-70% of treated women remain colonized at delivery 2

By following this evidence-based approach to antibiotic selection for GBS in pregnancy, clinicians can significantly reduce the risk of early-onset neonatal GBS infections by as much as 80-95% 3.