Half-life of IV oxytocin?
Correct Answer: 3 minutes
Description: Ans. b (3 minutes) (Ref. KDT 6th/320; Williams Obstetrics 22nd/Ch. 22; p. 540)KDT 6th/320 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 mU/min.- 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 mU/min has no apparent risks.# Contraindications and S/Es 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.
Category:
Gynaecology & Obstetrics
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