Clonidine pharmacokinetics in pregnancy.

The objective of this study was to determine the pharmacokinetic parameters of clonidine during pregnancy compared with previously published data in nonpregnant subjects. Serial blood and urine samples were collected in 17 women during mid to late pregnancy over one steady-state dosing interval to determine clonidine noncompartmental pharmacokinetic parameters (n = 17) and creatinine clearance. In six of these pregnant subjects, maternal and umbilical cord (venous and arterial) plasma samples were collected at the time of delivery for measurement of clonidine concentrations. Clonidine apparent oral clearance was found to be 440 +/- 168 ml/min during pregnancy compared with 245 +/- 72 ml/min as previously reported in nonpregnant subjects (p < 0.0001) (Cunningham et al., 1994). There was a strong correlation (r = 0.82, p < 0.001) between clonidine renal clearance, adjusted for variation in glomerular filtration rate, and urine pH. Umbilical cord to maternal plasma clonidine concentration ratios were 1.0 +/- 0.1 (arterial) and 1.0 +/- 0.1 (venous). In conclusion, clonidine is cleared more rapidly in pregnant women than in nonpregnant subjects. At the time of delivery, the fetus is exposed to similar plasma clonidine concentrations as the mother.