Pharmacokinetics and dosing requirements of digoxin in pregnant women treated for fetal supraventricular tachycardia.

BACKGROUND: The objective of this study was to characterize the pharmacokinetics (PK) of digoxin in pregnant women and its potential implications for drug dosing.

METHODS: Serum digoxin concentrations (SDCs) obtained in pregnant women treated for fetal supraventricular tachycardia (SVT) was retrospectively collected. PK analysis was comparatively performed using a two-stage approach (PKS™) and a Population PK approach (NONMEM™). As clinical outcome the fetal heart rate was recorded.

RESULTS: A total of 42 SDCs were obtained from 8 women in the 3rd trimester of pregnancy (mean age 33.0 years). The PK parameters estimated by both two-stage (volume of distribution (Vd) = 682.0 L, CV = 47.5%; serum clearance (CL) = 16.1 L/h, CV = 19%) and population approaches (Vd = 731.3 L, CV = 30.5%; CL = 18.7 L/h, CV = 17.8%) are very similar and show a clear trend of increasing drug disposition in the third trimester of pregnancy. An oral loading dose of 0.5 mg/8 h during 24 h followed by a maintenance regimen of 0.5 mg/12 h been recommended to start treatment.

CONCLUSIONS: Despite the small population, these parameters could be used as a guide to calculate the initial dosage requirements in the third trimester of pregnancy for treating fetal SVT. In addition, maternal SDCs should be routinely monitored for dosage adjustment purposes.