Maternal and transplacental pharmacokinetics of cefazolin

Objective: To evaluate the intrapartum pharmacokinetics of cefazolin, inclu ding delivery to amniotic fluid (AF) and fetal compartments, and to ascerta in that adequate cefazolin concentrations are attained to exceed the mean c oncentration inhibiting 90% (MIC90) of group B streptococcus strains. Methods: Cefazolin (1 g) was administered intravenously at five separate ti me intervals (0.5, 1, 2, 4, and 6 hours) before elective cesarean at tern t o 26 women with intact membranes and with no significant infections or card iovascular, liver, or renal disease. Samples of maternal blood, cord blood, and AF were obtained at the time of delivery. Exact collection times relat ive to cefazolin infusion were noted. Amniotic fluid contaminated with bloo d or meconium was excluded. Cefazolin concentration was measured by high-pr essure liquid chromatography. Results: All maternal and cord plasma cefazolin levels, except one, were ab ove the MIC90 for Streptococcus agalactiae (group B streptococcus). For AF, all cefazolin levels, except two, were above the MIC90. Conclusions: Cefazolin concentrations greater than or equal to the NHC,, fo r group B streptococcus were attained in nearly all maternal, fetal, and AF samples. This information, together with the knowledge that there is rare resistance of group B streptococcus to cefazolin, supports the use of cefaz olin as a better alternative than clindamycin or erythromycin for group B s treptococcus prophylaxis in patients with a nonanaphylactic penicillin alle rgy. (Obstet Gynecol 2001;98:1075-9. (C) 2001 by the American College of Ob stetricians and Gynecologists.).