Preterm Labor

Question 1

Terbutaline

Answer 1

Preterm Labor
ß-2-receptor adrenergic agonist (semi-selective)
MOA
- Causes myometrial relaxation by binding with ß-2 adrenergic receptors
ADE
- increase maternal heart rate and stroke volume
- peripheral vasodilation
- diastolic hypotension
- bronchial relaxation.
C/I
o “Injectable Terbutaline should not be used in pregnant women for prevention or prolonged treatment (beyond 48-72 hours) of PTL…bc of the potential for serious maternal heart problems & death.”
o “Oral Terbutaline should not be used for prevention or any treatment of PTL bc it has not been shown to be effective and has similar safety concerns.”

Question 2

Nifedipine

Answer 2

Preterm Labor
Calcium Channel Blockers
MOA
• directly block the influx of calcium ions through the cell membrane.
- inhibit release of intracellular calcium from the sarcoplasmic reticulum and increase calcium efflux from the cell.
- The resulting decrease in intracellular free calcium leads to inhibition of calcium-dependent myosin light-chain kinase phosphorylation and results in myometrial relaxation.

Question 3

Indomethacin (NSAID)

Answer 3

Preterm Labor
Cyclooxygenase inhibitors
MOA
- non-specific inhibitor of COX 1 and 2
- decrease prostaglandin production resulting in myometrial relaxation.
ADE (fetus)
– In utero constriction of ductus arteriosus, oligohydramnios

Question 4

Magnesium Sulfate

Answer 4

Preterm Labor
Indications
• Tocolysis: Inhibition of uterine contractions (not used for this much anymore)
• Preeclampsia/Eclampsia: *Anticonvulsant
• Given to mother in preterm labor as a *NEUROPROTECTIVE agent for the preterm infant
MOA
• Ca antagonist = decreases Ca influx into cell or release of Ca from SR → results in uterine relaxation
ADE (fetus)
- affects bone development
- possible teratogenic effects