title: Penicillin levels following the administration of benzathine penicillin G in pregnancy.
abstract: OBJECTIVE
  To investigate the distribution of penicillin in the maternal-placental-fetal unit at term gestation.
  
  
  METHODS
  Twenty-five healthy gravidas at 38-39 weeks' gestation scheduled for elective repeat cesarean delivery under spinal anesthesia received benzathine penicillin G, 2.4 million units intramuscularly (IM) preoperatively. Ten women delivered 1 day after injection, five delivered 2-3 days after, and ten delivered 7 days after. We collected maternal serum and cerebrospinal fluid, amniotic fluid (AF), and cord serum at delivery. Penicillin levels were measured using a validated agar disc diffusion method (sensitivity 0.006 micrograms/mL) with Micrococcus lutea as the test organism.
  
  
  RESULTS
  There was no significant difference in mean penicillin levels at day 1, day 2-3, or day 7 for maternal serum, maternal cerebrospinal fluid, cord serum, or AF. The mean (+/- standard error) penicillin concentration (range 0.005-0.59 micrograms/mL) in maternal serum declined from 0.14 +/- 0.04 micrograms/mL 1 day after injection to 0.08 +/- 0.06 micrograms/mL 7 days after injection. The proportion of patients with a penicillin concentration at or above 0.018 micrograms/mL in the maternal serum declined significantly from day 1 to day 7 (P = .03). Overall, nine of 25 women (36%) had serum penicillin levels that were less than 0.018 micrograms/mL.
  
  
  CONCLUSIONS
  A wide range of penicillin levels were observed in gravidas at term in the maternal serum, cerebrospinal fluid, umbilical cord serum, and AF within 1 week after 2.4 million units of benzathine penicillin G IM. We speculate that altered pharmacokinetics may affect the efficacy of this drug for prevention of congenital syphilis in the near-term gestation.
authors.affiliation: Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas.
authors.forename: L
authors.initials: L
authors.lastname: Nathan
authors.forename: R E
authors.initials: RE
authors.lastname: Bawdon
authors.forename: J E
authors.initials: JE
authors.lastname: Sidawi
authors.forename: R W
authors.initials: RW
authors.lastname: Stettler
authors.forename: D M
authors.initials: DM
authors.lastname: McIntire
authors.forename: G D
authors.initials: GD
authors.lastname: Wendel
mesh_terms: D000328:Adult; D000653:Amniotic Fluid / Q000737:chemistry*; D005260:Female; D005312:Fetal Blood / Q000737:chemistry*; D006801:Humans; D010401:Penicillin G Benzathine / Q000008:administration & dosage / Q000493:pharmacokinetics*; D010406:Penicillins / Q000032:analysis*; D011247:Pregnancy / Q000097:blood / Q000134:cerebrospinal fluid / Q000378:metabolism*
chemical_list: D010406:Penicillins; D010401:Penicillin G Benzathine