RITODRINE HYDROCHLORIDE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for RITODRINE HYDROCHLORIDE (RITODRINE HYDROCHLORIDE).
Beta-2 adrenergic receptor agonist; stimulates beta-2 receptors in uterine smooth muscle, causing relaxation and inhibiting uterine contractions.
| Metabolism | Hepatic metabolism via phase II conjugation (glucuronidation) and minor oxidation; not significantly metabolized by CYP450. |
| Excretion | Renal: 70-90% as unchanged drug and metabolites (mainly glucuronide and sulfate conjugates); biliary/fecal: minor (<10%). |
| Half-life | Terminal elimination half-life: 1.7-2.6 hours (mean 2.0 h) in pregnant women; prolonged in renal impairment. |
| Protein binding | ~90-93% bound to albumin (α1-acid glycoprotein also contributes). |
| Volume of Distribution | Vd: 1.5-2.5 L/kg (pregnant women); indicates extensive tissue distribution. |
| Bioavailability | Oral: ~30% (due to first-pass metabolism); IM: ~80%; IV: 100%. |
| Onset of Action | IV: rapid (within minutes); IM: 5-10 minutes; oral: 30-45 minutes. |
| Duration of Action | IV/IM: 2-4 hours (dose-dependent); oral: 3-6 hours. Clinical tocolytic effect may persist longer. |
Intravenous: Initial 0.1 mg/min, increased by 0.05 mg/min every 10-15 min until contractions cease or intolerance; max 0.35 mg/min. Oral: 10-20 mg every 2-4 hours, start 30 min before IV discontinuation.
| Dosage form | INJECTABLE |
| Renal impairment | Creatinine clearance <30 mL/min: reduce dose by 50%; not studied in severe impairment. |
| Liver impairment | Child-Pugh class B or C: contraindicated due to risk of hepatic encephalopathy. |
| Pediatric use | Not FDA-approved for pediatric use; off-label: IV 0.1 mg/min, titrate up to 0.35 mg/min; oral 10 mg every 2-4 hours. |
| Geriatric use | No specific dose adjustment, but monitor for tachycardia and electrolyte imbalances due to reduced renal function. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for RITODRINE HYDROCHLORIDE (RITODRINE HYDROCHLORIDE).
| Breastfeeding | Ritodrine is excreted into breast milk, with a milk-to-plasma (M/P) ratio estimated at approximately 2.6 to 4.3 based on limited data. Because it can cause cardiovascular effects in the infant (e.g., tachycardia, jitteriness), it is generally not recommended during breastfeeding. Alternate tocolytics with better safety profiles should be considered. |
| Teratogenic Risk | Ritodrine hydrochloride is classified as FDA Pregnancy Category B. Animal studies have not demonstrated fetal harm, but there are no adequate, well-controlled studies in pregnant women. It is used as a tocolytic agent to suppress preterm labor. There is no evidence of teratogenic effects when used in the second and third trimesters; however, potential risks include maternal tachycardia, pulmonary edema, and fetal tachycardia. First-trimester exposure data are limited, and the drug is not typically used during this period. Fetal risks include hyperinsulinemia and hypoglycemia after birth due to beta-adrenergic stimulation. |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypersensitivity to ritodrine or any component.","Maternal conditions: cardiac disease, tachyarrhythmias, uncontrolled hypertension, hyperthyroidism, pheochromocytoma.","Fetal conditions: intrauterine infection, fetal distress where continuation of pregnancy is contraindicated.","Preeclampsia/eclampsia.","Placental abruption or major uterine bleeding."]
| Precautions | ["Maternal pulmonary edema risk, especially with fluid overload; monitor fluid balance.","Cardiovascular effects: tachycardia, hypotension, arrhythmias; use caution with heart disease.","Hyperglycemia and hypokalemia may occur; monitor blood glucose and electrolytes.","May cause fetal acidosis; use with caution in intrauterine growth restriction.","Risk of maternal hypoglycemia after infusion discontinuation."] |
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| Fetal Monitoring | Maternal monitoring includes continuous assessment of heart rate, blood pressure (risk of hypotension or hypertension), serum glucose (due to hyperglycemic effect), serum potassium (risk of hypokalemia), and signs of pulmonary edema (dyspnea, crackles). Fetal monitoring includes continuous fetal heart rate monitoring to detect fetal tachycardia and non-stress test assessment. Fluid intake and output should be recorded to avoid fluid overload. |
| Fertility Effects | Ritodrine hydrochloride is not indicated for fertility purposes. There are no well-documented studies on fertility effects in humans. In animal studies, no impairment of fertility was observed at doses up to 50 mg/kg/day, which is approximately 50 times the maximum human daily dose. However, as a beta-adrenergic agonist, it may theoretically alter reproductive hormone profiles, but this is not clinically significant in standard tocolytic use. |