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Chapter 64

Drugs That Affect Uterine Function

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Drugs That Affect Uterine Function

Three main categories: Uterine relaxants (tocolytics)

• Uterine relaxation• Suppression of preterm labor

Uterine stimulants (oxytocics)• Uterine contraction• Induction/augmentation of labor• Control of postpartum bleeding• Induction of abortion

Drugs used to decrease menorrhagia (heavy menstrual bleeding)

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Preterm Birth

Before 37 weeks’ gestation Leading cause of infant morbidity and

neonatal mortality United States: 12.5% of all live births Premature births account for 75% of all

neonatal mortalities and 50% of congenital neurologic deficits

Most common neonatal respiratory distress syndrome

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Uterine Relaxants (Tocolytics)

Used to delay delivery Average delay: only 48 hours If used with glucocorticoids, the

glucocorticoids can accelerate lung development

Also used to buy time to treat infection

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Control of Myometrial Contraction

Regulated by multiple mediators Beta-adrenergic agonists Oxytocin Prostaglandins

Four classes of drugs: all decrease the availability of phosphorylated light chain Beta-adrenergic antagonists, calcium channel

blockers, cyclooxygenase (COX) inhibitors, and oxytocin-receptor antagonists

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Uterine Relaxants (Tocolytics)

Beta2-selective adrenergic agonist Terbutaline (Brethine)

• Beta2-selective adrenergic agonist• Not approved by FDA for this use

Nifedipine (Procardia, Adalat, Nifedical) Can suppress labor for up to 48 hours Efficacy equals that of terbutaline, and safety is

superior

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Uterine Relaxants (Tocolytics)

Indomethacin (Indocin) Second-line tocolytic Higher risk for neonatal complications Prolonged renal insufficiency, bronchopulmonary

dysplasia, necrotizing enterocolitis, and periventricular leukomalacia

Nitroglycerin, a nitric oxide donor

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Uterine Relaxants (Tocolytics)

Atosiban Oxytocin: receptor antagonist

Magnesium sulfate High dose does not prevent or delay preterm birth

but does increase infant mortality Was previously used readily Low-dose magnesium sulfate may reduce the risk

of cerebral palsy without increasing mortality

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Drugs Used to Promote Cervical Ripening

Dinoprostone (Prepidil, Cervidil) Dinoprostone gel Dinoprostone vaginal inserts (Cervidil) Misoprostol (Cytotec)

Not approved for this use

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Uterine Stimulants (Oxytocics)Prostaglandins: Dinoprostone and Misoprostol

(can also induce labor) Dinoprostone

Most widely used for cervical ripening Shortens duration of labor, allows reduced dosage

of oxytocin, decreases need for cesarean section Can also induce abortion

Misoprostol Not approved for cervical ripening More convenient and less expensive than

dinoprostone Higher incidence of uterine tachysystone

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Uterine Stimulants (Oxytocics)

Three groups of uterine stimulants Oxytocin Ergot alkaloids Prostaglandins

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Uterine Stimulants (Oxytocics)

Oxytocin (Pitocin) Peptide hormone produced by the posterior

pituitary Increases the force, frequency, and duration of

uterine contractions Uterus becomes progressively more responsive to

oxytocin throughout pregnancy Facilitates labor, but unclear whether it can initiate

labor

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Uterine Stimulants (Oxytocics)

Oxytocin (Pitocin) (cont’d) Physiologic and pharmacologic effects

• Uterine stimulation• Milk ejection• Water retention

Precautions and contraindications• Uterine rupture may occur• Women with active genital herpes

Adverse effect: water retention/intoxication

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Uterine Stimulants (Oxytocics)

Ergot alkaloids: ergonovine and methylergonovine Dried preparation of Claviceps purpurea Stimulate adrenergic, dopaminergic, and

serotonergic receptors Not used to induce labor (sustained contractions) Can cause constriction of arterioles and veins and

risk of severe hypertension Used to control postpartum bleeding

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Uterine Stimulants (Oxytocics)

Ergot alkaloids: ergonovine and methylergonovine (cont’d) Therapeutic uses

• Postpartum bleeding (not responsive to oxytocin and carboprost tromethamine)

• Augmentation of labor• Migraine

Adverse effects (IV administration)• Hypertension

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Uterine Stimulants (Oxytocics)

Carboprost tromethamine (Hemabate) Preferred agent for controlling postpartum

hemorrhage Causes intense uterine contractions Adverse effects

• GI reactions• Vomiting and diarrhea• Fever• Vasoconstriction• Constriction of the bronchi

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Drugs for Menorrhagia

Tranexamic acid Menorrhagia Trauma patients Adverse effects and interactions

NSAIDs Combination oral contraceptives Levonorgestrel-releasing intrauterine system