What are alternative treatments for Group B streptococcal (GBS) infection in pregnant women with a penicillin allergy?

Alternative Antibiotics for Group B Streptococcus Prophylaxis in Penicillin-Allergic Pregnant Women

For pregnant women with penicillin allergy requiring GBS prophylaxis, cefazolin is the preferred alternative for those without high-risk allergy symptoms, while clindamycin (if susceptible) or vancomycin should be used for those at high risk for anaphylaxis. 1

Risk Stratification of Penicillin Allergy

The first critical step is determining the patient's risk for anaphylaxis based on allergy history:

High-risk for anaphylaxis includes: 1

• History of immediate hypersensitivity reactions (anaphylaxis, angioedema, or urticaria)
• History of asthma or other conditions that would make anaphylaxis more dangerous

Low-risk allergy symptoms include: 2

• Isolated rash, itching, or nausea
• Remote or unclear history of penicillin reaction

Approximately 10% of persons with penicillin allergy also have immediate hypersensitivity reactions to cephalosporins, making this risk assessment essential. 1

Treatment Algorithm for Low-Risk Penicillin Allergy

Cefazolin is the agent of choice for women not at high risk for anaphylaxis: 1, 3

• Dosing: 2 g IV initial dose, then 1 g IV every 8 hours until delivery
• Rationale: Narrow spectrum of activity, achieves high intraamniotic concentrations, and GBS isolates remain highly susceptible with minimum inhibitory concentrations consistently <0.5 µg/ml 1, 4

Treatment Algorithm for High-Risk Penicillin Allergy

For women at high risk for anaphylaxis, the approach depends on susceptibility testing results:

If GBS isolate is susceptible to both clindamycin AND erythromycin: 1, 3

• Clindamycin: 900 mg IV every 8 hours until delivery
• Alternative: Erythromycin 500 mg IV every 6 hours until delivery 1

If susceptibility testing unavailable, results unknown, or isolate resistant to clindamycin/erythromycin: 1, 3

• Vancomycin: 1 g IV every 12 hours until delivery
• Vancomycin should be reserved for cases where no other options exist due to concerns about promoting antimicrobial resistance 1, 4

Critical Importance of Susceptibility Testing

Susceptibility testing for clindamycin and erythromycin must be performed on prenatal GBS isolates from penicillin-allergic women at high risk for anaphylaxis. 1, 3

The rationale is compelling:

• Resistance rates to clindamycin range from 8-28% and to erythromycin from 14-30% in recent studies 5, 6
• Co-resistance is extremely common: 92% of erythromycin-resistant strains are also clindamycin-resistant 6
• Inducible clindamycin resistance occurs in 5.8-8.6% of isolates that appear susceptible to clindamycin but resistant to erythromycin 5, 6

Testing for inducible clindamycin resistance (D-test) is necessary for isolates susceptible to clindamycin but resistant to erythromycin. 3

Common Pitfalls and How to Avoid Them

Pitfall #1: Using clindamycin or erythromycin without susceptibility testing

• This occurs frequently, with 63% of penicillin-allergic women receiving alternative antibiotics 2
• These antibiotics should never be used without confirmed susceptibility due to high resistance rates 6

Pitfall #2: Failing to verify penicillin allergy history

• Many reported penicillin allergies are not true IgE-mediated reactions 1
• Verification is important because alternatives to penicillin have broader spectrum, higher cost, and unproven efficacy 1
• Pregnant women with reported penicillin allergy should undergo skin testing when possible, as this provides both short- and long-term health benefits 7

Pitfall #3: Treating GBS colonization before labor

• Antimicrobial agents should NOT be used before the intrapartum period to treat GBS colonization 1, 3
• Such treatment is ineffective in eliminating carriage, does not prevent neonatal disease, and may cause adverse consequences including resistance 1, 3

Pitfall #4: Using second-generation cephalosporins

• Cefoxitin resistance has been reported among GBS isolates 1
• Only first-generation cephalosporins (cefazolin) should be used 1

Special Populations

Women with GBS bacteriuria during pregnancy: 3

• Require treatment of the UTI when diagnosed
• Still need intrapartum antibiotic prophylaxis during labor regardless of earlier treatment
• Should receive prophylaxis even if bacteriuria was treated earlier in pregnancy

Planned cesarean delivery before labor/rupture of membranes: 1

• These women are at low risk for early-onset GBS disease
• Should not routinely receive intrapartum chemoprophylaxis