Pharmacokinetics of ritodrine administered intravenously: recommendations for changes in the current regimen.
We define the pharmacokinetics of ritodrine in 13 pregnant women who received the drug intravenously. With constant infusion of 50 micrograms/minute, steady state ritodrine concentrations reached 28 +/- 11 ng/ml (SD) with a range of 15 to 45 ng/ml. This wide variation is a result of differences in plasma clearance, which ranged from 1.0 to 3.3 L/min, mean 1.94 +/- 0.71 L/min. The apparent volume of distribution was 6.95 +/- 3.54 L/kg, indicating that ritodrine is extensively bound to extravascular tissue. When an infusion of ritodrine is stopped, plasma concentrations fall rapidly initially with a distribution half-life of 5.9 +/- 6.0 minutes. After the initial rapid fall, plasma concentrations decrease more slowly with a mean disposition half-life of 156 +/- 51 minutes. On the basis of the pharmacokinetic parameters defined, we recommend that the current infusion regimen for ritodrine be changed. The infusion rate of ritodrine should start at 50 micrograms/minute rather than 100 micrograms/minute. The maximal infusion rate of 350 micrograms/minute should be increased and once labor is inhibited, the infusion rate should be reduced.
Caritis
S N
SN
Department of Obstetrics and Gynecology, University of Pittsburgh School of Medicine, PA.
Venkataramanan
R
R
Darby
M J
MJ
Chiao
J P
JP
Krew
M
M
D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D007262:Infusions, Intravenous; D008657:Metabolic Clearance Rate; D011247:Pregnancy / Q000378:metabolism*; D012312:Ritodrine / Q000008:administration & dosage / Q000009:adverse effects / Q000493:pharmacokinetics*
D012312:Ritodrine