Maternal-fetal transfer of cefazolin in the first twenty weeks of pregnancy.

Maternal-fetal transfer of cefazolin was investigated with use of a single 14-mg/kg intramuscular dose administered to 40 gravidas before elective hysterectomy. The half-life of cefazolin in maternal serum was 1.5 hr with mean concentrations at 2 and 4 hr of 39 and 16 microgram/ml, respectively. By microbiological assay, cefazolin was not detected in brain, cerebrospinal fluid, lung, liver, or kidney of the fetus but was present in concentrations of 1-11 microgram/ml in 12 of 27 individual samples of fetal serum from 0.75 to 10.66 hr. Cefazolin appeared in fetal urine from 2.17 to 19.5 hr at levels of less than 5 microgram/ml with a half-life of 5.4 hr. Cefazolin was present in the amniotic fluid of fetuses older than 14 weeks in concentrations of less than 1 microgram/ml from 9 to 21.75 hr. After administration of a single dose to the mother early in pregnancy, the fetal distribution of cefazolin is limited to the body fluids.