title: Tacrolimus placental transfer at delivery and neonatal exposure through breast milk.
abstract: OBJECTIVE
  The current investigation aims to provide new insights into fetal exposure to tacrolimus in utero by evaluating maternal and umbilical cord blood (venous and arterial), plasma and unbound concentrations at delivery. This study also presents a case report of tacrolimus excretion via breast milk.
  
  
  METHODS
  Maternal and umbilical cord (venous and arterial) samples were obtained at delivery from eight solid organ allograft recipients to measure tacrolimus and metabolite bound and unbound concentrations in blood and plasma. Tacrolimus pharmacokinetics in breast milk were assessed in one subject.
  
  
  RESULTS
  Mean (±SD) tacrolimus concentrations at the time of delivery in umbilical cord venous blood (6.6 ± 1.8 ng ml(-1)) were 71 ± 18% (range 45-99%) of maternal concentrations (9.0 ± 3.4 ng ml(-1)). The mean umbilical cord venous plasma (0.09 ± 0.04 ng ml(-1)) and unbound drug concentrations (0.003 ± 0.001 ng ml(-1)) were approximately one fifth of the respective maternal concentrations. Arterial umbilical cord blood concentrations of tacrolimus were 100 ± 12% of umbilical venous concentrations. In addition, infant exposure to tacrolimus through the breast milk was less than 0.3% of the mother's weight-adjusted dose.
  
  
  CONCLUSIONS
  Differences between maternal and umbilical cord tacrolimus concentrations may be explained in part by placental P-gp function, greater red blood cell partitioning and higher haematocrit levels in venous cord blood. The neonatal drug exposure to tacrolimus via breast milk is very low and likely does not represent a health risk to the breastfeeding infant.
authors.affiliation: Department of Pharmaceutics, University of Washington, Seattle, WA, USA.
authors.forename: Songmao
authors.initials: S
authors.lastname: Zheng
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Easterling
authors.forename: Karen
authors.initials: K
authors.lastname: Hays
authors.forename: Jason G
authors.initials: JG
authors.lastname: Umans
authors.forename: Menachem
authors.initials: M
authors.lastname: Miodovnik
authors.forename: Shannon
authors.initials: S
authors.lastname: Clark
authors.forename: Justina C
authors.initials: JC
authors.lastname: Calamia
authors.forename: Kenneth E
authors.initials: KE
authors.lastname: Thummel
authors.forename: Danny D
authors.initials: DD
authors.lastname: Shen
authors.forename: Connie L
authors.initials: CL
authors.lastname: Davis
authors.forename: Mary F
authors.initials: MF
authors.lastname: Hebert
mesh_terms: D000328:Adult; D001942:Breast Feeding; D036861:Delivery, Obstetric; D005260:Female; D005312:Fetal Blood / Q000737:chemistry; D006801:Humans; D007166:Immunosuppressive Agents / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics* / Q000627:therapeutic use; D007231:Infant, Newborn; D008895:Milk, Human / Q000737:chemistry*; D016377:Organ Transplantation; D010920:Placenta / Q000378:metabolism*; D021041:Placental Circulation; D011247:Pregnancy; D016559:Tacrolimus / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics* / Q000627:therapeutic use
chemical_list: D007166:Immunosuppressive Agents; D016559:Tacrolimus
keywords: breast milk; neonatal exposure; placental transfer; pregnancy; tacrolimus; unbound drug concentration