(ri' toe dreen)
Pregnancy Category B
- β2- selective adrenergic agonist
- Tocolytic drug (uterine relaxant)
A β-receptor agonist that acts relatively selectively to inhibit contractility of uterine smooth muscle.
- Management of preterm labor in selected patients ≤20 wk gestation
- Contraindications: hypersensitivity to ritodrine or components of preparation (injection contains sodium metabisulfite; some patients are allergic to sulfites); pregnancies of shorter duration than 20 wk; antepartum hemorrhage; eclampsia and severe preeclampsia; intrauterine fetal death; chorioamnionitis; maternal cardiac disease; pulmonary hypertension; maternal hyperthyroidism; uncontrolled maternal diabetes mellitus; preexisting maternal medical conditions that would be seriously affected by a β-adrenergic agonist, such as hypovolemia, cardiac arrhythmias associated with tachycardia or digitalis toxicity, uncontrolled hypertension, pheochromocytoma, bronchial asthma already treated by betamimetics or steroids.
Available Forms: Injection--10, 15 mg/mL; injection in 5% Dextrose--0.3 mg/mL
Individualize dosage by balancing uterine response and unwanted effects. The following is a guide to safe and effective dosage.
0.05 mg/min IV initially (0.33 mL/min or 20 drops/min using a microdrip chamber at the recommended dilution; see below). Gradually increase by 0.05 mg/min (10 drops/min) every 10 min until desired result is attained. Usual effective dosage is between 0.15 and 0.35 mg/min (30---70 drops/min) continued for at least 12 h after uterine contractions cease.
Metabolism: Hepatic, T1/2: 1.7---2.6 h
Distribution: Crosses placenta; enters breast milk
- Preparation: Empty the contents of three ampuls (50 mg/ampul; total of 150 mg) into 500 mL of compatible IV diluent to make a solution of 0.3 mg/mL concentration. Compatible diluents are 0.9% Sodium Chloride Solution, 5% Dextrose Solution; 10% Dextran 40 in 0.9% Sodium Chloride Solution, 10% Invert Sugar Solution, Ringer's Solution, Hartmann's Solution. Store at room temperature; protect from excessive heat. Do not use after 48 h. Do not use IV solution that is discolored or contains precipitate or particulate matter.
- Infusion: Use a controlled infusion device to administer IV infusions; an IV mi-crodrip chamber (60 drops/mL) can provide a convenient range of infusion rates.
- CNS: Headache, weakness, tremor, nervousness, restlessness, emotional upset, anxiety, malaise
- GI: Nausea, vomiting, ileus, constipation, diarrhea
- CV: Increase in heart rate, increase in systolic BP, decrease in diastolic BP, palpitations, chest pain, supraventricular tachycardia, sinus bradycardia with withdrawal of drug
- Respiratory: Dyspnea, hyperventilation, postpartum pulmonary edema (sometimes fatal)
- Hypersensitivity: Anaphylactic shock, rash
- Other: Erythema, transient elevation blood glucose, hypokalemia
- GI: Ileus
- CV: Fetal heart rate increase, hypotension in neonates whose mothers were given other β-adrenergic agonists
- Hematologic: Hypoglycemia, hypocalcemia in neonates whose mothers were given other β-adrenergic agonists
Clinically important interactions
- Increased sympathomimetic effects with other sympathomimetic drugs
- Decreased therapeutic effects with β-adrenergic blockers
- Potentially fatal pulmonary edema with corticosteroids
History: Hypersensitivity to ritodrine or components of preparation, pregnancy, antepartum hemorrhage, eclampsia and severe preeclampsia, intrauterine fetal death, chorioamnionitis, maternal cardiac disease, pulmonary hypertension, maternal hyperthyroidism, uncontrolled maternal diabetes mellitus, hypovolemia, cardiac arrhythmias, uncontrolled hypertension, pheochromocytoma, bronchial asthma already treated by betamimetics or steroids
Physical: Maternal and fetal heart rate, maternal BP and R, plasma glucose and electrolytes (potassium)
- Monitor maternal P, R closely; persistent maternal P > 140 beats/min or persistent tachypnea (R > 20/min) may be signs of impending pulmonary edema.
- Avoid fluid overload; serial hemograms may indicate state of hydration.
- Maintain patient in left lateral position during the infusion to minimize hypotension.
Drug-specific teaching points
- Report chest pain, dizziness, insomnia, weakness, tremor or irregular heart beat.
Adverse effects in Italic are most common; those in Bold are life-threatening.