From the Guidelines
Penicillin G is the first-line antibiotic for group B streptococcus (GBS) infections, typically administered intravenously at 5 million units initially, followed by 2.5-3 million units every 4 hours until delivery for intrapartum prophylaxis. For patients with non-severe penicillin allergy, cefazolin 2g IV initially, then 1g every 8 hours is recommended 1. In cases of severe penicillin allergy, clindamycin 900mg IV every 8 hours or vancomycin 1g IV every 12 hours can be used, with clindamycin preferred for GBS isolates known to be susceptible to clindamycin 1.
Key Considerations
- The choice of antibiotic should be guided by the patient's allergy history and the susceptibility of the GBS isolate 1.
- For women colonized with clindamycin-resistant GBS isolates who are allergic to penicillin and at high risk of anaphylaxis, vancomycin is recommended 1.
- Early-onset GBS antibiotic prophylaxis is effective within two to four hours of administration, and penicillin G and ampicillin continue to be recommended for intrapartum antibiotic prophylaxis 1.
Special Populations
- Infants born earlier than 35 weeks’ gestation are at highest risk of early-onset sepsis and early-onset GBS disease, and performing a blood culture and starting antibiotic treatment are recommended even after sufficient intrapartum antibiotic prophylaxis 1.
- For non-pregnant adults with GBS infections, treatment depends on the site and severity, but typically includes penicillin G, ampicillin, or ceftriaxone for 10-14 days 1.
Rationale
GBS is naturally susceptible to penicillins because these antibiotics inhibit cell wall synthesis in the bacteria 1. Adequate treatment is crucial as GBS can cause serious infections in newborns, pregnant women, elderly individuals, and those with compromised immune systems or chronic conditions. Treatment should begin promptly upon diagnosis to prevent complications and reduce transmission risk, particularly during childbirth to prevent neonatal infection 1.
From the Research
Antibiotics for Group B Strep
- Group B streptococci (GBS) are the leading cause of life-threatening neonatal bacterial infections in developed countries 2.
- The risk of early neonatal GBS infection increases in cases of preterm delivery, maternal fever during delivery, and membrane rupture more than 18 hours before delivery 2.
- Intrapartum antibiotic prophylaxis in women who carry Group B streptococci reduces the risk of early-onset neonatal GBS infection from 4.7% to 0.4% (p = 0.02) 2.
- Penicillin G (benzylpenicillin) is the antibiotic of choice, while penicillin A (ampicillin or amoxicillin) is an alternative 2.
- In case of penicillin allergy, erythromycin or clindamycin are generally active against Group B streptococci and carry no particular risks for the infant 2.
Effectiveness of Intrapartum Antibiotic Prophylaxis
- The effectiveness of 4 or more hours of prophylaxis with penicillin or ampicillin was high among term (91%, 95% confidence interval [CI] +63% to +98%) and preterm (86%, 95% CI +38% to +97%) neonates 3.
- Effectiveness was significantly lower for clindamycin (22%, 95% CI -53% to +60%) 3.
- Beta-lactam prophylaxis given 4 or more hours before delivery is highly effective for prevention of early-onset GBS disease 3.
Antibiotic Choice for Group B Streptococcus Prophylaxis
- Pregnant individuals who report a penicillin allergy were more likely to receive alternative antibiotics for GBS prophylaxis compared to those without a penicillin allergy 4.
- This was associated with an increased frequency of postnatal blood draws among neonates of mothers with a reported penicillin allergy 4.
- Cefazolin may offer equivalent efficacy and safety compared to standard penicillin prophylaxis 5.
- Women who received cefazolin prophylaxis had the highest negative culture rate (95.2%, 197/207) 5.
Maternal and Neonatal Outcomes
- There were no significant differences in maternal and neonatal outcomes among the IAP groups 5.
- Neonates of patients who received alternative GBS prophylaxis were significantly more likely to undergo a postnatal lab draw compared to neonates of patients who received beta-lactam antibiotics 4.
- Among neonates whose mothers received appropriate compared with inappropriate antibiotics, there were no differences in Apgar score, number of blood draws, antibiotic use, length of hospital stay, or composite morbidity 6.