Antibiotics for Group B Strep Prophylaxis

Choice of antibiotic[11] – It is important to review the sensitivity patterns of bacteria in your local area or health authority.

Ampicillin, Penicillin G, Cefazolin, Clindamycin, and Vancomycin

For treating asymptomatic Group B Strep, the midwife may order these antibiotics following the Perinatal Services of BC (PSBC) or other appropriate hospital protocol. All of these antibiotics have similar activity against GBS and all cross the placenta. Ampicillin, having a broader spectrum of anti-microbial activity than Penicillin, may be more likely to lead to selection or resistant organisms than would widespread use of Penicillin.

Group B streptococcus (GBS) bacteria is a gram-positive coccus commonly found in the gastrointestinal tract. It is estimated that between 10 and 30% are colonized with the Group B streptococcus at any given time including at the time of birth. The GBS bacteria can migrate out of the digestive tract and into the vaginal canal and into the urethra and colonize the bladder. GBS bacteriuria occurs in 2% to 4% of all pregnancies and is associated with urinary tract disease (see Antibiotics for Urinary Tract Infection above), endometritis, wound infection and an increased risk of neonatal disease. Heavy colonization of GBS has been associated with preterm labour and preterm premature rupture of membranes. GBS can potentially cause devastating complications for the newborn infant such as sepsis, pneumonia, meningitis and death.

The antibiotic regimen of choice for intrapartum chemoprophylaxis is intravenous Penicillin G or Ampicillin. Penicillin G is generally considered preferable to Ampicillin. If allergic to Penicillin, intravenous Cefazolin may be administered if low risk for anaphylaxis, or intravenous Clindamycin if high risk for anaphylaxis and the GBS is confirmed to be sensitive to Clindamycin, or intravenous Vancomycin if at high risk for anaphylaxis and the GBS is not sensitive to Clindamycin. If Vancomycin is being considered, an antenatal referral for penicillin skin testing to confirm the penicillin allergy is recommended. The incidence of anaphylactic reaction to Penicillin ranges from .04 to .004 (4 in 10,000 to 4 in 100,000).

11. Drug Information Lexicomp. (n.d.). Ampicillin, Penicillin G, Cefazolin, Clindamycin, Vancomycin drug information. Retrieved from