Transplacental passage of vancomycin from mother to neonate.

Objective: The objective of the study was to analyze a large number of patients receiving vancomycin chemoprophylaxis and evaluate the maternal and neonatal cord blood levels at the time of delivery.

Study Design: Every mother who entered labor with a positive group B streptococcal culture and a high-risk penicillin allergy with resistance to clindamycin or unknown sensitivity was consented to participate in the study. In the initial phase of the study, patients received the standard intravenous dose of 1 g every 12 hours. Based on the results, this was changed to a dosing of 15 mg/kg every 12 hours in the second phase and then further modified to 20 mg/kg every 8 hours in the third phase. Maternal and cord blood vancomycin levels were obtained at delivery and evaluated.

Results: A total of 55 patients consented to participate in the study, with 31 in phase I, 12 in phase II, and 12 in phase III. For the standard-dosing phase I group, only 32% of maternal and 9% of cord blood samples were therapeutic at delivery. For phase II, 50% of maternal and 33% of cord blood values were therapeutic; however, in phase III, 83% of mothers and neonates had therapeutic levels at the time of delivery.

Conclusion: With standard dosing, only 9% of neonates have therapeutic vancomycin levels at delivery. By using a regimen of 20 mg/kg intravenous every 8 hours (maximum individual dose 2 g), the newborn therapeutic level increases above 80%. The pharmacological pattern shows that transplacental passage occurs with fetal levels equaling maternal levels, but transplacental transport is somewhat slow in both directions.