Vaginal group B streptococcus status during intrapartum antibiotic prophylaxis

Abstract

Objective: To assess maternal group B streptococcus (GBS) colonization status and the pharmacokinetic profile of penicillin G in the umbilical cord and amniotic fluid compartment during 4 hours of intrapartum antibiotic prophylaxis (IAP).

Methods: In a prospective study at a hospital in Montevideo, Uruguay, 60 GBS carriers in active labor after a singleton pregnancy of 37 weeks or more were enrolled between April 1, 2011, and April 30, 2012. Intravenous penicillin G was administered via a standard regimen. Rectovaginal samples were obtained before IAP initiation, and 2 and 4 hours after the initial dose. Penicillin G concentrations were measured by high-performance liquid chromatography. Samples were obtained from fetal cord blood in all cases and from amniotic fluid obtained from patients who delivered by cesarean.

Results: Among the 60 participants, 43 (72%) had a positive rectovaginal sample before IAP initiation. Of these women, 23 (53%) had negative cultures after 2 hours; after 4 hours, only 5 (12%) remained positive for GBS. The penicillin G concentration in amniotic fluid and cord blood was above the minimum inhibitory concentration (0.12 μg/mL) in all cases.

Conclusion: Four hours of IAP was needed to reduce the number of women with positive GBS cultures to 12%. Therefore, 4 hours of IAP might be necessary to achieve overall effectiveness from this treatment.

Keywords: Group B streptococcus; Intrapartum antibiotic prophylaxis; Penicillin.