Umbilical Cord and Maternal Serum Levels of Mezlocillin in Term and Preterm Deliveries in Mothers Diagnosed with Chorioamnionitis

Recent investigations have demonstrated decreased morbidity in the newborn following maternal administration of antibiotics to mothers with a diagnosis of chorioamnionitis. These benefits are based upon transplacental passage of antibiotics. Fifteen preterm and term women with the diagnosis of chorioamnionitis were given 3 or 4 g of mezlocillin intravenously every 4 to 6 h. Maternal serum and umbilical cord samples were collected at delivery and the concentrations of antibiotics were determined by high-pressure liquid chromatography. Peak serum levels of mezlocillin in the cord and mother occurred within 60 min, but were eliminated more rapidly in the mother. Umbilical cord levels, while initially lower with the 3 g dose, were present longer than 4 hr for both regimens. Placental transfer of antibiotics appeared to be affected by the aging placenta with decreased initial levels and slower fetal clearance at term.