Pharmacokinetics of betamethasone after maternal or fetal intramuscular administration.
OBJECTIVE
The purpose of this study was to determine the pharmacokinetics of betamethasone in maternal and fetal circulations after maternal or fetal intramuscular administration.


METHODS
Ewes that bore single fetuses underwent surgery at approximately 96 days of pregnancy for the implantation of fetal and maternal vascular catheters. At approximately 103 days, five ewes were injected intramuscularly with betamethasone (0.5 mg/kg body weight) or five fetuses received ultrasound-guided intramuscular injections of betamethasone (0.5 mg/kg estimated fetal weight). Maternal and fetal blood samples were collected serially for the measurement of plasma betamethasone concentrations.


RESULTS
Fetal injection caused higher peak fetal betamethasone concentrations (341.2+/-23.7 nmol/L) than maternal injection (37.6+/-3.7 nmol/L; P<.001) and greater cumulative betamethasone exposure. The half-life of betamethasone in the fetal circulation was shorter after fetal injection (1.1+/-0.3 hours) than after maternal injection (8.5+/-2.0 hours; P=.006).


CONCLUSIONS
The duration of fetal and maternal exposure to betamethasone can be minimized by direct fetal intramuscular administration that, in sheep, affords lung maturation without adverse effects on fetal growth.
Moss
Timothy J M
TJ
Lotteries Commission Perinatal Research Laboratories, School of Women's and Infants' Health, University of Western Australia, Box M094, 35 Stirling Highway, Crawley, WA 6009, Australia. tmoss@cyllene@uwa.edu.au
Doherty
Dorota A
DA
Nitsos
Ilias
I
Harding
Richard
R
Newnham
John P
JP
D000704:Analysis of Variance; D000818:Animals; D001623:Betamethasone / Q000008:administration & dosage / Q000493:pharmacokinetics*; D005260:Female; D005333:Fetus / Q000187:drug effects*; D007273:Injections, Intramuscular; D008431:Maternal-Fetal Exchange / Q000187:drug effects*; D023421:Models, Animal; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000187:drug effects*; D011336:Probability; D012680:Sensitivity and Specificity; D012756:Sheep; D018709:Statistics, Nonparametric; D014018:Tissue Distribution
D001623:Betamethasone