Intrapartum antibiotic prophylaxis 1: relative effects of recommended antibiotics on gram-negative pathogens.

OBJECTIVE: To assess whether the antibiotic chosen for intrapartum antibiotic prophylaxis affects the subsequent exposure of the neonate to ampicillin-resistant gram-negative bacteria.

METHODS: We performed a randomized clinical trial of ampicillin versus penicillin for intrapartum antibiotic prophylaxis. Genital tract cultures for Enterobacteriaceae were obtained at study entry and 8-36 hours postpartum. Organisms were isolated, identified, and tested for ampicillin susceptibility.

RESULTS: The ampicillin (n = 175) and penicillin (n = 177) groups, respectively, did not differ in rates of ampicillin-resistant Escherichia coli at entry (25% versus 22%, P =.57) or postpartum (36% versus 38%, P =.64). Similarly, groups did not differ in rates of ampicillin-resistant Enterobacteriaceae at entry (38% versus 32%, P =.23) or postpartum (51% versus 55%, P =.46). However, postpartum culture rates of resistant Escherichia coli were higher than entry culture rates for both the ampicillin (36% versus 25%, P =.026) and penicillin (38% versus 22%, P <.001) groups. Postpartum culture rates of resistant Enterobacteriaceae were also higher than entry culture rates for both the ampicillin (51% versus 38%, P <.001) and penicillin (55% versus 32%, P <.001) groups. Results were similar when considering only women who received two or more doses and no additional antibiotics.

CONCLUSION: Intrapartum antibiotic prophylaxis with either ampicillin or penicillin increases exposure of neonates to ampicillin-resistant Enterobacteriaceae.