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RGU 2 > Pharmacology of Obstetrical Agents > Flashcards

Pharmacology of Obstetrical Agents Flashcards

1
Q

What is a UTEROTONIC agen?

A
  • PROMOTES contractions of uterine smooth muscle.
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2
Q

What is a TOCOLYTIC agent?

A
  • SUPPRESSES contractions of uterine smooth muscle.
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3
Q

When would you want to ENHANCE uterine contraction?

A
  • induction of labor (before spontaneous contractions) in order to limit an extended pregnancy, if her membranes rupture w/o labor, gestational HTN or DM, prevent early rupture of membrane, or to aid in placental insufficiency.
  • augmentation of labor
  • therapeutic abortion
  • POST-PARTUM HEMORRHAGE (PPH) control
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4
Q

What is the leading cause of maternal mortality worldwide?

A
  • PPH
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5
Q

When would you want to SUPPRESS uterine contraction?

A
  • prevent/delay premature labor
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6
Q

What are the 4 phases of molecular control of uterine activity?

A
  • Phase 1 (quiescence)= progesterone
  • Phase 2 (activation)= estrogen
  • Phase 3 (stimulation)= prostaglandins
  • Phase 4 (involution)= oxytocin
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7
Q

What are the major categories of uterotonic agents?

A
  • prostaglandins (PGE and PGF2a)
  • oxytocin
  • progesterone receptor antagonists
  • ergots
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8
Q

Which of the major uterotonic agents are used for cervical ripening and induction?

A
  • prostaglandins (PGE and PGF2a)
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9
Q

Which of the uterotonic agents are used for mostly induction/augmentation?

A
  • oxytocin, progesterone receptor antagonists, and ergots
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10
Q

What are the major categories of tocolytic agents?

A
  • progesterone (preventative)
  • MgSO4
  • Ca2+ channel blockers
  • oxytocin antagonists
  • B-adrenergic agonists
  • prostaglandin synthesis (COX) inhibitors
  • nitric oxide donors
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11
Q

What is the general mechanism in myometrial cells leading to contraction (aka smooth muscle cell contraction)?

A
  • AP depolarizes myometrial cell membrane.
  • opening of voltage-gated Ca2+ channels and entry of Ca2+.
  • Ca2+ binds calmodulin.
  • activates myosin light-chain kinase (MLCK).
  • enables interaction of myosin with actin needed for contraciton.
  • MLCP (phosphatase) will then dephosphorylate myosin leading to relaxation.
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12
Q

Do agents that PROMOTE uterine contraction tend to increase or decrease free cytosolic Ca2+ concentration?

A
  • increase
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13
Q

Do agents that PREVENT uterine contraction tend to increase or decrease free cytosolic Ca2+ concentration?

A
  • decrease
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14
Q

What are some MATERNAL contraindications for uterotonic agents?

A
  • unfavorable prior uterine incision type.
  • contracted or distorted pelvic anatomy.
  • abnormally implanted placentas
  • active infection or cervical cancer
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15
Q

What are some FETAL contraindications for uterotonic agents?

A
  • substantial macrosomia
  • severe hydrocephalus
  • malpresentation
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16
Q

What can happen from prolonged stimulation of uterine contraction?

A
  • persistent uteroplacental insufficiency
  • sinus bradycardia
  • arrhythmias
  • fetal death
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17
Q

What does progesterone do to prostaglandins?

A
  • decreases them (makes sense since progesterone maintains pregnancy).
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18
Q

Will PGE and PGF2 be high or low during labor?

A
  • HIGH
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19
Q

What is the most common use for prostaglandins?

A
  • make labor more effective by increasing the efficacy of induction.
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20
Q

Are prostaglandins more or less effective than oxytocin for uterine contractions during the 2nd trimester?

A
  • MORE effective
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21
Q

What is the mechanism of action of prostaglandins?

A
  1. increase IP3-mediated Ca2+ release from SR.
  2. increase frequency of APs, thus increasing Ca2+ entrhy through VGCCs.
  3. activate non-specific cation channels (increasing Ca2+).
  4. PGEs activate MLCK and inactivate MLCP by blocking adenylyl cyclase (cAMP, PKA).
  5. PGF2a may also increase Ca2+ sensitivity of apparatus.
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22
Q

** What is DINOPROSTONE? (SKETCHY or PICMONIC)

A
  • naturally occurring PGE2 used for vaginal ripening.

- available as a gel or time-released vaginal insert

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23
Q

** What is MISOPROSTOL? (SKETCHY or PICMONIC)

A
  • PGE1 analogue used for vaginal ripening (off-label use).
  • cheaper than dinoprostone.
  • shorter half life (so easier to manage).
  • can be vaginal or oral
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24
Q

Does dinoprostone or misoprostol have higher rates of uterine contraction abnormality?

A
  • misoprostol
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25
Q

** What is CARBPROST TROMETHAMINE? (PICMONIC)

A
  • synthetic analogue of PGF2a.
  • also upregulates oxytocin receptors and gap junctions in myometrium to promote contractions.
  • used for 2nd trimester abortion.
26
Q

What are the ADRs of the prostaglandins?

A
  • uterine tachysystole (greater than 5 contractions in a 10 min period).
  • fever
  • retained placental fragments
27
Q

In what patients must you heed caution when using prostaglandins?

A
  • asthmatics and uncontrolled BP because these will cause smooth muscle contraction everywhere (including bronchioles and arterioles).
28
Q

** What is OXYTOCIN (pitocin)? (PICMONIC)

A
  • most common induction agent.

- hormone made in the hypothalamus (usually made along with ADH) and stored and released by POSTERIOR pituitary.

29
Q

Why is oxytocin so much better at the end of pregnancy?

A
  • bc the oxytocin receptors increase 300 fold.
30
Q

Can oxytocin (pitocin) be used after delivery to control uterine hemorrhage?

A

YES

31
Q

*** What is the mechanism of action for oxytocin?

A

same as prostaglandins increasing IP3-mediated Ca2+ release from SR, but it also INHIBITS Ca2+ efflux from the cell.

  • also directly inhibit MLCP.
  • also stimulates release of PGE2 and F2a
  • all increasing Ca2+ and thus contraction.
32
Q

What is an ADR of oxytocin?

A
  • H2O intoxication, secondary to its ADH-like effects
33
Q

** What is MIFEPRISTONE? (PICMONIC under methotrexate)

A
  • competitive progestin antagonist, thus inducing uterine contractions.
  • sensitizes uterus to contractile prostaglandins (sometimes thus given with misoprostol).
34
Q

** What is METHYLERGONOVINE? (PICMONIC)

A
  • “Ergot” uterotonic agent produced by a fungus that causes disease in plants.
  • directly stimulates uterine smooth muscle and induces arterial vasoconstriction.
  • NOT for long-term use.
35
Q

What is the mechanism of action of METHYLERGONOVINE?

A
  • partial agonist of alpha1-adrenergic receptors and has some 5-HT (serotoning) and dopamine receptor activity.
  • inhibits the release of endothelial-derived relaxation factor (EDRF).
36
Q

What is an ADR of METHYLERGONOVINE if overused?

A
  • Ergot poisoning leading to gangrene in the nursing infant.
37
Q

How long do the TOCOLYTIC agents usually last?

A
  • most only 48 hrs, but once labor starts none can hold off labor for more than 7 days. They usually provide enough of time to give steroids to get fetal lungs producing surfactant.
38
Q

What does progesterone do to smooth muscle membranes?

A

HYPERpolarizes, silencing myometrial contractility.

39
Q

** Why do the progesterone levels of the placenta remain so high during pregnancy?

A
  • it lacks 17a-hydroxylase (which would allow conversion of progesterone to estrogen down the line).
  • note: the placenta does make estrogens from fetal androgens.
40
Q

** What leads to progesterone withdrawal and thus labor?

A
  • INCREASED PRA:PRB ratio (progesterone receptors). PRA inhibits progesterone action in the myometrium, thus leading to progesterone withdrawal.
  • INCREASED ER-alpha expression
41
Q

How does progesterone decrease myometrial contractility?

A
  1. decreased Ca2+ entry and release from SR.
  2. can act through nuclear and membrane PRs to alter gene expression, decreasing contractility of myometrial cells by preventing gap junctions.
  3. membrane PRs couple to Ca2+ signaling pathways.
  4. inhibits PG synthesis.
42
Q

What progesterone is given to maintain progesterone levels needed for uterine quiescence?

A
  • 17 alpha-hydroxyprogesterone caproate (17-OHPC)
  • however, may not work well bc the progesterone withdrawal is mediated by receptor changes, which will be there regardless.
43
Q

When should 17 alpha-hydroxyprogesterone NOT be used?

A
  • in women pregnant with multiples
44
Q

What are some contraindications for progesterone?

A
  • coagulopathy
  • breast cancer
  • liver problems
  • uncontrolled HTN
45
Q

*** What is the first line tocolytic in the US?

A
  • MgSO4
46
Q

*** What is the mechanism by which MgSO4 prevents uterine contraction?

A
  • antagonizes/competes with Ca2+
  • decreases extracellular Ca2+
  • increases Ca2+-dependent ATPase, promoting Ca2+ uptake by SR.
  • inhibits release of acetylcholine at neuromuscular junctions.
  • activates adenylate cyclase
  • increases NO synthase
47
Q

What can magnesium toxicity do?

A
  • loss of patellar reflex
  • respiratory depression
  • respiratory paralysis
  • cardiac arrest
  • in that order as concentration increases
48
Q

** What is NIFEDIPINE?

A
  • voltage-gated Ca2+ channel blocker

* longest acting tocolytic (can delay labor for 7 days), but off-label use.

49
Q

What is ATOSIBAN?

A
  • competitive inhibitor of oxytocin receptors and vasopressin (ADH) receptors.
  • NOT approved in US.
50
Q

*** How do B-adrenergic agonists work?

A
  • activate adenylyl cyclase, increasing cAMP and thus PKA, leading to phosphorylation and INACTIVATION of MLCK= decreased contractility
  • decreases Ca2+ concentration.
51
Q

What is the only B-adrenergic agonist used, but rarely anymore?

A
  • Terbutaline (B2-agonist)

* Risk of post-partum hemorrhage due to occupation of receptor for a long time.

52
Q

What COX inhibitor is sometimes used as a tocolytic?

A
  • INDOMETHACIN= NSAID that decreases prostaglandin synthesis.
  • can cause premature closure of fetal ductus arteriosus.
53
Q

What is glyceryl trinitrate patch or nitroclycerine?

A
  • NO= vasodilator, which increases cGMP leading to blocked Ca2+ entry.
  • will INACTIVATE MLCK
  • not really used
54
Q

What are the newer studies of tocolytics looking at?

A
  • synergy (combining these drugs to be able to achieve the same effects at lower doses).
55
Q

What are galactogogues?

A
  • drugs that stimulate lactation
56
Q

What stimulates lactation?

A
  1. nipple stimulation (from suckling) stimulates mechanoreceptors that trigger the hypothalamus.
  2. hypothalamus stimulates PROLACTIN= milk production from ANTERIOR PITUITARY; and OXYTOCIN= milk release (let-down) from POSTERIOR PITUITARY.
57
Q

** Will thyrotropin releasing hormone and estrogen stimulate or inhibit prolactin release?

A
  • STIMULATE
58
Q

** Will dopamine stimulate or inhibit prolactin release?

A
  • INHIBIT
59
Q

What are some herbal supplements that are galactogogues?

A
  • FENUGREEK
  • fennel
  • asparagus
  • got’s rue
  • anise
60
Q

What drugs will inhibit dopamine D2 receptors, thus increasing prolactin?

A

antipsychotics:

  • METOCLOPRAMIDE
  • Chlorpromazine (may alter CNS development so NOT recommended)
61
Q

How does oxytocin cause milk release?

A
  • contracts the myoepithelial cells around the alveoli and milk ducts.
  • delivered nasally
62
Q

What is CABERGOLINE?

A
  • D2 receptor agonist, thus inhibiting lactation. Used for prolactinomas.
  • ADRs= HTN, stroke, seizures and psychosis.

RGU 2 (24 decks)

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