Objective: To evaluate the intrapartum pharmacokinetics of cefazolin, including delivery to amniotic fluid (AF) and fetal compartments, and to ascertain that adequate cefazolin concentrations are attained to exceed the mean concentration inhibiting 90% (MIC(90)) of group B streptococcus strains.
Methods: Cefazolin (1 g) was administered intravenously at five separate time intervals (0.5, 1, 2, 4, and 6 hours) before elective cesarean at term to 26 women with intact membranes and with no significant infections or cardiovascular, liver, or renal disease. Samples of maternal blood, cord blood, and AF were obtained at the time of delivery. Exact collection times relative to cefazolin infusion were noted. Amniotic fluid contaminated with blood or meconium was excluded. Cefazolin concentration was measured by high-pressure liquid chromatography.
Results: All maternal and cord plasma cefazolin levels, except one, were above the MIC(90) for Streptococcus agalactiae (group B streptococcus). For AF, all cefazolin levels, except two, were above the MIC(90).
Conclusions: Cefazolin concentrations greater than or equal to the MIC(90) for 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 cefazolin as a better alternative than clindamycin or erythromycin for group B streptococcus prophylaxis in patients with a nonanaphylactic penicillin allergy.