Exam 11: Oxytocics Flashcards
What hormone ratio is important in promoting parturition?
Increased estrogen to progesterone
What hormone prevents contractions throughout pregnancy?
Progesterone
Two mechanisms behind progesterone preventing uterine contractions
- Hyperpolarizing membrane potential of smooth muscle cells
2. Promoting Ca2+ storage in the sarcoplasmic reticulum
3 mechanisms behind estrogen promoting contractions
- Induction of Na+ channels
- Induction of gap junctions
- Induction of oxytocin receptors
What causes softening/ripening of the cervix for parturition?
Prostaglandins
3 uses for Oxytocics
- Induction or augmentation of labor
- Control of postpartum uterine hemorrhage (the number 1 cause of maternal mortality)
- Induction of abortion or expulsion of dead fetus after intrauterine death
2 uses of Tocolytics
- Delay or prevention of preterm labor
2. Slow or arrest delivery so therapeutic actions can be taken
Definition of pre-term labor
Before 37 weeks
Contractions every 10 minutes lasting 30 seconds
Chemical composition of Oxytocin
Nonapeptide (9 amino acids)
Oxytocin mechanism
Gq (increased calcium, phospholipase C)
What causes increased sensitivity of the uterus to oxytocin in gestation?
Estrogen
Goal of IV oxytocin in labor induction
3-5 contractions of 60-90 seconds per 10 minute period without fetal distress
Most common indication for Oxytocin use in labor induction
Prolonged pregnancy (42 weeks)
4 reasons for oxytocin labor induction
- Mother or fetus is at risk and you need to deliver now
- Premature rupture of membranes
- Prolonged pregnancy
- Selective induction (mom’s choice)
Oxytocin effects on breast
Contracts myoepithelial cells forcing milk out of the alveoli of the breast
CV side effects of Oxytocin
Hypotension
tachycardia
arrhythmia
Electrolyte abnormality associated with Oxytocin use
Hyponatremia due to antidiuretic effect and water retention
Can lead to seizures and death
Serious fetal complication associated with oxytocin use
Sustained contraction/hyperstimulation can interfere with fetal circulation
Oxytocin contraindications (3)
- Abnormal fetal position
- Fetal distress
- Previous uterine surgery
What happens to prostaglandin production in pregnancy?
Increases in the 3rd trimester from the placenta and endometrium
PG effect on the uterus (mechanism)
Cause contractions by mediating an increase in intracellular calcium
PG effects on cervix (mechanism)
Cervical ripening by increasing secretion of collagenase
Dinoprostone
PGE2
Prepidil, Cervidil
PGE2 preparations used for cervical ripening
2 side effects of PGE2 preparations (prepidil, cervidil)
- GI disturbance
2. Uterine hyperstimulation
PGE2 contraindications
Same as oxytocin
- Abnormal fetal position
- Fetal distress
- Previous uterine surgery
15-methyl PGF2alpha (Carbaprost) Tromethamine
2 uses
2nd line drug to control postpartum bleeding after oxytocin or ergot alkaloids
Can also induce abortion in the second trimester
Misoprostol
PGE1 analog
Used to terminate early pregnancies (up to 49 days from LMP)
Promotes uterine contractions and causes detatchment
Ergonovine and Methylergonovine
Ergot Alkaloids
Binds alpha-1 receptors, causing an increase in Ca2+ and uterine contractions
Used for postpartum or post abortion bleeding
Ergonovine and Methylergonovine uses
Postpartum or post abortion bleeding
DO NOT use for labor induction or augmentation
Ergot alkaloid side effects
Think alpha 1
HTN due to vasoconstriction
NVD
Gangrene of the fingers/toes
Ergot alkaloid contraindications
HTN
CV disease
Liver or kidney disease
Mifepristone
Progesterone antagonist
Mifepristone use, mechanism
Termination of pregnancy up to 49 days from LMP
Progesterone antagonist
Causes detachment of the products of conception
Sodium Chloride 20%, urea 40 50% injection mechanism
Damages mucosa of uterus causing release of Prostaglandins leading to uterine contractions
Sodium Chloride 20%, urea 40 50% injection use
late term abortions
FDA approved tocolytic agent
There isn’t one
When are tocolytics used/
to delay premature labor up to 24 hours in patients between 24 and 34 weeks gestation
Indomethacin
PG-synthetase inhibitor
use to prevent labor at weeks 24-32.
Dont use it after 32 weeks or you may cause closure of ductus arteriosus and oligohydramnios
nifedipine mechansim
inhibits contractions by decreasing intracellular calcium
Nifedipine use in pregnancy
used as a tocolytic between 32-34 weeks because you wouldn’t want to use indomethacin that late
Terbutaline
B2 agonist
Inhibits contraction
Very dangerous to mother and fetus
Difficult to dose correctly
Mg sulfate
Tocolytic
decreases intracellular calcium
Not very effective at delaying birth
