Usage
- Ritodrine is prescribed to stop or delay premature labor (labor that begins before 37 weeks of pregnancy).
- Pharmacological Classification: Uterine relaxant, beta-2 adrenergic agonist.
- Mechanism of Action: Ritodrine relaxes the uterine muscles by stimulating beta-2 adrenergic receptors, decreasing the intensity and frequency of uterine contractions. This helps prolong the pregnancy to allow for fetal development.
Alternate Names
- Yutopar (former brand name, no longer available in the US)
How It Works
- Pharmacodynamics: Ritodrine primarily affects the uterus, causing relaxation and reducing the intensity and frequency of contractions. It also affects the cardiovascular system, potentially causing increased heart rate and decreased blood pressure. It can also cause metabolic changes like hyperglycemia and hypokalemia.
- Pharmacokinetics:
- Absorption: Rapid absorption after oral administration. Bioavailability is about 30%.
- Distribution: Crosses the placenta.
- Metabolism: Primarily hepatic, by conjugation with glucuronic acid or sulfate.
- Elimination: Primarily renal (70-90%).
- Mode of Action: Binds to beta-2 adrenergic receptors on uterine smooth muscle cells, activating adenylate cyclase, increasing intracellular cyclic AMP (cAMP), leading to decreased myosin light chain kinase activity and reduced muscle contraction.
- Receptor Binding: Beta-2 adrenergic receptor agonist.
Dosage
Standard Dosage
Adults (for premature labor):
Intravenous:
- Initial dose: 50-100 mcg/min, titrated every 10 minutes in 50 mcg increments until contractions subside or maternal heart rate reaches 130 bpm.
- Maintenance dose: 150-350 mcg/min, titrated to the lowest effective dose.
Oral (following IV therapy):
- Initial dose: 10 mg every 2 hours for the first 24 hours.
- Maintenance dose: 10-20 mg every 4-6 hours.
- Maximum daily dose: 120 mg.
Children: Not routinely used in children. Limited data exists for pediatric dosing.
Special Cases:
- Elderly Patients: Use with caution; dosage adjustments may be necessary.
- Patients with Renal Impairment: Caution advised.
- Patients with Hepatic Dysfunction: Caution advised.
- Patients with Comorbid Conditions (e.g., diabetes, cardiovascular disease, hyperthyroidism): Use with caution. Monitor closely for adverse effects.
Clinical Use Cases: Ritodrine is primarily indicated for the management of preterm labor in a hospital setting where continuous monitoring is feasible. It is not typically used for intubation, surgical procedures, mechanical ventilation, general ICU use, or emergency situations.
Dosage Adjustments: Adjust dosage based on uterine activity, maternal heart rate, blood pressure, and other side effects. Close monitoring is essential.
Side Effects
Common Side Effects:
- Increased heart rate (tachycardia)
- Palpitations
- Headache
- Nervousness/anxiety
- Nausea/vomiting
- Tremors
- Dizziness/drowsiness
- Dry mouth
- Flushing
- Sweating
Rare but Serious Side Effects:
- Pulmonary edema
- Cardiac arrhythmias
- Myocardial ischemia
- Hypokalemia
- Hyperglycemia
- Hepatotoxicity
- Psychiatric symptoms
Long-Term Effects: Not typically used for extended periods.
Contraindications
- Antepartum hemorrhage
- Eclampsia or severe preeclampsia
- Intrauterine fetal death
- Chorioamnionitis
- Cardiac disease
- Placenta previa
- Abruptio placentae
- Cord compression
- Hypersensitivity to ritodrine
Drug Interactions
- Beta-blockers (e.g., atenolol, propranolol)
- Corticosteroids (e.g., prednisone, hydrocortisone)
- Sympathomimetics (e.g., epinephrine, dopamine)
- Potassium-depleting drugs
- Some antihypertensives
- Certain medications for irregular heartbeats
- Several other drugs; always check for potential interactions before co-prescribing.
Pregnancy and Breastfeeding
- Pregnancy Safety Category: Limited evidence exists for use before 20 weeks gestation and should be avoided if possible. Potential fetal risks include tachycardia, hypoglycemia or hyperglycemia at birth.
- Breastfeeding: Not recommended due to lack of safety data. Ritodrine may be excreted in breast milk.
Drug Profile Summary
- Mechanism of Action: Beta-2 adrenergic agonist, relaxes uterine smooth muscle.
- Side Effects: Tachycardia, palpitations, headache, nervousness, nausea, vomiting, pulmonary edema (rare).
- Contraindications: See Contraindications section above.
- Drug Interactions: Beta-blockers, corticosteroids, sympathomimetics, many others (see Drug Interactions section).
- Pregnancy & Breastfeeding: Use with caution after 20 weeks gestation if benefits outweigh risks. Not recommended for breastfeeding.
- Dosage: See Dosage section above.
- Monitoring Parameters: Maternal heart rate, blood pressure, uterine activity, fetal heart rate, blood glucose, potassium levels.
Popular Combinations
- Not typically used in combination therapy for preterm labor due to increased risk of side effects. Corticosteroids may be given to enhance fetal lung maturity.
Precautions
- General Precautions: Close monitoring of maternal and fetal well-being. Careful evaluation of risk/benefit ratio.
- Specific Populations:
- Pregnant Women: Monitor closely. Not recommended for use prior to 20 weeks gestation.
- Breastfeeding Mothers: Not recommended.
- Lifestyle Considerations: Avoid alcohol.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Ritodrine?
A: See the detailed Dosage section above. Dosage is dependent on the route of administration (IV vs. oral) and must be titrated according to patient response and tolerance.
Q2: What are the common side effects of Ritodrine?
A: Common side effects include tachycardia, palpitations, headache, nervousness, nausea, vomiting, tremors.
Q3: What are the serious side effects of Ritodrine?
A: Serious side effects can include pulmonary edema, cardiac arrhythmias, hypokalemia. These require immediate medical attention.
Q4: Can Ritodrine be used in patients with diabetes?
A: Use with caution in patients with diabetes as it can exacerbate hyperglycemia. Close monitoring of blood glucose is crucial.
Q5: Is Ritodrine safe to use during breastfeeding?
A: Ritodrine is not recommended during breastfeeding due to lack of safety data and potential excretion in breast milk.
Q6: What are the contraindications to using Ritodrine?
A: Contraindications include conditions where prolonging pregnancy would be harmful, such as antepartum hemorrhage, eclampsia/severe preeclampsia, fetal demise, chorioamnionitis, as well as certain cardiac conditions.
Q7: What are the important drug interactions to consider with Ritodrine?
A: Ritodrine can interact with beta-blockers, corticosteroids, sympathomimetics, and potassium-depleting drugs among others. A thorough medication review is essential before co-prescribing.
Q8: How is Ritodrine administered?
A: Ritodrine can be administered intravenously or orally. Intravenous administration is typically used initially for acute management of preterm labor, followed by oral therapy if needed.
Q9: How does Ritodrine work to stop premature labor?
A: Ritodrine relaxes the uterine smooth muscle by binding to beta-2 adrenergic receptors, reducing the frequency and intensity of uterine contractions.
