OB TRIAD
Calcium Channel Blocker
Preterm labor tocolysis
Hypotension
Myocardial depressionTocolytic agents. Parenteral agents may prolong pregnancy, but for no more
than 72 h. This does provide a window of time for (1) administration of
maternal IM betamethasone to enhance fetal pulmonary surfactant and (2)
transportation of mother and fetus in utero to a facility with neonatal intensive
care. Oral tocolytic agents are no more effective than placebo.
Magnesium sulfate is a competitive inhibitor of calcium. Clinical
monitoring is based on decreasing but maintaining detectable deep tendon
reflexes. Side effects include muscle weakness, respiratory depression, and
pulmonary edema. Magnesium overdose is treated with IV calcium
gluconate. Contraindications include renal insufficiency and myasthenia
gravis.
β-adrenergic agonists (e.g., terbutaline). Tocolytic effect depends on
the β2-adrenergic receptor myometrial activity. Side effects include
hypertension, tachycardia, and possible hyperglycemia, hypokalemia, and
pulmonary edema. Contraindications include cardiac disease, diabetes
mellitus, uncontrolled hyperthyroidism.
Calcium-channel blockers (e.g., nifedipine) decrease intracellular
calcium. Side effects include tachycardia, hypotension, and myocardial
depression. Contraindications include hypotension.