Oxytocics and Tocolytics

Question 1

Oxytocics

Answer 1

drugs that stimulate uterine smooth muscle to contract

- induce labor, control post-partum hemorrhage

Question 2

Tocolytics

Answer 2

any drug used to suppress uterine smooth muscle and suppress labor

Question 3

Smooth muscle contraction and Ca

Answer 3

GPC -> PLC -> PIP2 -> IP3 and DAG -> Ca influx

• MLC kinase -> cross-bridge facilitated by Ca-calmodulin
• Ca actively pumped out of cell
• MLC and dephosphorylated by MLCPas

Question 4

Oxytocin

Answer 4

synthesized in paraventricular nucleus of hypothalamus
- released from vesicles in response to cervical dilation, stimulation of vagina, suckling
- Oxytocin receptor (GPCR) -> PLC
Absorption and Excretion - parenteral and sublingual -> can’t be given orally

Question 5

Pitocin

Answer 5

synthetic oxytocin -> drug of choice for labor induction
- milk let down post-partum
- stimulation of uterine motility to reduce bleeding
Contraindications -> cephalo-pelvic disproportion, hypertonic uterine contractions

Question 6

Prostaglandins

Answer 6

PLA2 -> releases arachidonic acids from phospholipids
- accomplished by COX pathway
- function close to site of synthesis and are deactivated to inactive metabolites
- levels rise in amniotic fluid during parturition, induces contractions, promotes cervical ripening
INDOMETHACIN -> reduces oxytocin induced uterine contractions through reducing PG production

Question 7

PG Drugs

Answer 7

Dinoprostone -> natural PGE
Misoprostol -> synthetic PGE
Dinoprost -> natural PGF2
Carboprost -> PGF2 (injection)

Question 8

Ergots

Answer 8

alkaloids from fungus
- potent smooth muscle stimulating properties are capitalized in medicine
Ergonovine/Ergometrine -> contraction of uterus
Ergotamine -> contraction of blood vessels

Question 9

Tocolytics (beta2 agonists)

Answer 9

beta 2 selective agents -> activate adenylyl cyclase and raises cAMP
TERBUTALINE -> given after 20th week
- increase HR, pulmonary edema, hyperglycemia, MI
Magnesium sulfate -> competes with Ca and relaxes smooth muscle -> prevents seizures associated with eclampsia

Question 10

Oxytocin Receptor Antagonist

Answer 10

Atosiban -> only oxytocin receptor antagonist approved for use

• inhibits OTR inositol trisphosphate activation
• delays labor, rapid onset
• increased fetal mortality

Question 11

INDOMETHACIN

Answer 11

non-selective inhibitor of COX 1 and 2 -> blocks PG formation
- for short-term delay of labor