Oxytocics and Tocolytics Flashcards
Receptors targeted in premature contractions
Beta 2
Receptors targeted to induce labor
Alpha 1
Agents that stimulate uterine contraction
Oxytocics
Agents that relax the uterus
Tocolytics
When is labor induction considered
Typically it is only considered when the risks of continuing pregnancy without intervention are greater than the risks of induction
In small doses, oxytocin _________. At higher doses, it _________.
In small doses, oxytocin increases both the frequency and the force of uterine contractions. At higher doses, it produces sustained contraction.
Half life of oxytocin
5-15 minutes
How does oxytocin help post-partum blood loss
Post-partum blood loss can also be minimized using high dose oxytocin to stimulate a sustained contraction. Uterine contraction clamps off blood vessels and prevents further blood loss.
How is oxytocin used to “test” labor
A dose of oxytocin is administered to produce a short series of contractions, thus, placental blood flow to the fetus is transiently reduced, similar to true labor. The oxytocin challenge test measures the fetal heart rate response during this infusion and provides the physician information about placental circulatory reserve. An abnormal response, seen as specific decelerations in the fetal heart rate that is being co-monitored with administration of the drug, indicate fetal hypoxia or intolerability to labor and may indicate need for cesarean delivery.
How is oxytocin related to ADH
Both produced in the post. pituitary and has a very similar structure. Oxytocin can bind to ADH receptors, so high doses can lead to acute water intoxication (Hyponatremia) which can lead to convulsions, come, death
Role of prostoglandins in delivery
Prostaglandins cause cervical ripening (relaxation)
Mechanism of prostoglandin action
They alter the extracellular ground substance of the cervix and increase the activity of collagenase in the cervix. By increasing proteoglycan content and changing the biophysical properties of collagen, relaxation of cervical smooth muscle occurs.
Example of prostoglandin analogs
Dinoprostone - synthetic prostaglandin E2 analogs, vaginally inserted gel or tablet
Misoprostol (Cytotec) - synthetic PGE1 analog, vaginally inserted in tablet form
Carboprost (Hemabate) - synthetic 15-methylprostaglandin F2 analog, typically injected intramuscularly in an attempt to reduce post-partum hemorrhage, induces uterine contraction
Side effects of prostoglandin analogs
Side effects are typically limited to nausea, vomiting, fever
Two most common ergot alkaloids
Ergonovine and Methylergonovine.
Mechanism of ergot alkaloids
Ergot alkaloids act on alpha-1 adrenergic receptors, dopaminergic, and serotonin receptors.
When are ergot alkaloids used and why
Because it does not have a “specific target” it is difficult to tightly control its downstream effects, so although it does produce uterine contractility, it is only used for this purpose when controlling post-partum hemorrhage
Side effects of ergot alkaloids
vasospasm, nausea, vomiting, diarrhea, dizziness, arrhythmias, and hallucinations (similar to fungus responsible for LSD).
What is mifepristone
An anti-progesterone agent, casues uterine lining decay and producing uterine contraction
What is uterine tachysystole
hyperstimulation, more than five contractions in 10 minutes, which may result in placental abruption or uterine rupture.
Contraindications for induction of labor
When are tocolytics indicated, and most common classes
short-term prolongation of pregnanc
beta-adrenergic receptor agonists, calcium channel blockers or NSAIDs
What is Magnesium Sulfate (MgSO4) mostly used for
primary agent to prevent seizures associated with pre-eclampsia and for control of seizures with eclampsia
reduces the severity and risk of cerebral palsy in surviving infants if administered when birth is anticipated before 32 weeks of gestation
Used to be used as a tocolytic because it has a huge list of side effects
What is terbatuline and when is it used
β2 receptor adrenergic agonist
Used for short-term labor suppresors when inpatient because mother has top be monitored – can cause sympathetic side effects like hyotension, hyperglycemia, dizziness, anxiety
Also used to counter effects of oxytocin to “reverse” induced labor
What is indomethacin and when is it used
NSAID, used to block prostoglandins
Not used after 32 weeks because can cause premature closure of fetal ductus arteriosus which could be disastrous if the newborn has a cardiac anomaly that relies on its patency for oxygenation.
Examples of calcium channel blockers
Nifedipine, Procardia
Mechanism of calcium channel blockers
The Ca2+ channels are complex proteins composed of distinct subunits (α1, α2, β, δ and γ) encoded by multiple genes. Dihydropyridines (calcium channel blockers) such as nifedipine bind to voltage gated L-type channels and prevent intracellular calcium influx, thus decreasing contraction.
Side effects of calcium channel blockers
reduce mean arterial pressures through vasodilation throughout the body, so as expected, side effects that can be seen include hypotension, flushed skin, dizziness, and headache.
