<prompt> Half-life of IV oxytocin?1 minute3 minutes7 minutes9 minutes  <response>: Ans. b 3 minutes Ref. KDT 6th320; Williams Obstetrics 22ndCh. 22; p. 540KDT 6th320 and Internet:Oxytocin, produced by the hypothalamus and stored and secreted by the posterior pituitary gland, is a peptide of nine amino acids a nonapeptide. It is rapidly degraded in liver and kidney; plasma half life 6 minutes and is shortened at term.OXYTOCIN Oxytocin causes milk ejection, contraction of pregnant uterus.6 Oxytocin--mainly used for induction of labour. It is found that a uterine response to oxytoxin for inducting labour occurs within 3 to 5 minutes of beginning an oxytocin infusion and that a plasma steady state is reached in 40 minutes. Response depends on- preexisting uterine activity,- cervical status,- pregnancy duration, and- individual biological differences. The uterine response to oxytocin increases from 20 to 30 weeks and increases rapidly at term. Oxytocin should be discontinued if: Q- the number of contractions persists with a frequency greater than five in a 10-minute period or- seven in a 15-minute period or- with a persistent nonreassuring fetal heart rate pattern. The mean half-life of oxytocin is 5 minutes Q hence when it is stopped, its concentration in plasma rapidly falls. Maximal Dosage of oxytocin:- It is found that the likelihood of progression to a vaginal delivery decreases at and beyond an oxytocin dosage of 36 mUmin.- However, if contractions are not adequate--less than 200 Montevideo units--and if the fetal status is reassuring and labor has arrested, an oxytocin infusion dose greater than 48 mUmin has no apparent risks. Contraindications and SEs of oxytocin:ContraindicationsSide effectsa Grand multiparaUterine ruptureb Contracted pelvisHypotensionc MalpresentationAntidiuresisd Obstructed labourPituitary shocke Incoordinate uterine contractionsAnginal painf Hypovolemia and cardiac diseases Oxytocin Challenge test Syn: contraction stress test Indications are very selective- IUGR,- Post-maturity,- Pregnancy with DM,- Hypertension. Contraindications- Compromised foetus,- Previous ISCS- APH,- Threat of preterm labour It takes at least 1-2 hr to perform the test.Educational PointATOSIBAN Atosiban is an oxytocin receptor antagonist with high uterine specificity. 