title: Nifedipine pharmacokinetics during preterm labor tocolysis.
abstract: Nifedipine, a calcium entry blocker, has known relaxing effects on the myometrium. Thirteen women in preterm labor received nifedipine for tocolysis. Blood samples obtained serially during treatment and at the time of delivery were assayed for maternal and neonatal nifedipine concentrations. The peak concentration of nifedipine during sublingual therapy ranged from 23.4 to 197.9 ng/ml and reflected substantial interpatient variability. The mean (+/- SD) measurable trough value in patients who received 20 mg of nifedipine orally every 6 hours was 7.2 +/- 5.5 ng/ml. The maternal mean half-life of nifedipine was 81 minutes (range 49 to 137 minutes). At delivery, neonatal nifedipine levels were nondetectable in 6 of the 11 neonates available for study; in 5, values ranged from 29.5 to 1.8 ng/ml. From these results we conclude that both sublingual and oral nifedipine treatment results in variable but usually measurable maternal plasma concentrations and that placental transfer of nifedipine occurs.
authors.affiliation: Department of Gynecology and Obstetrics, Stanford University School of Medicine, California.
authors.forename: J E
authors.initials: JE
authors.lastname: Ferguson
authors.forename: T
authors.initials: T
authors.lastname: Schutz
authors.forename: R
authors.initials: R
authors.lastname: Pershe
authors.forename: D K
authors.initials: DK
authors.lastname: Stevenson
authors.forename: T
authors.initials: T
authors.lastname: Blaschke
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D009543:Nifedipine / Q000097:blood / Q000493:pharmacokinetics*; D007752:Obstetric Labor, Premature / Q000378:metabolism*; D011247:Pregnancy; D015145:Tocolysis; D015149:Tocolytic Agents / Q000097:blood / Q000493:pharmacokinetics*
chemical_list: D015149:Tocolytic Agents; D009543:Nifedipine