Ritodrine is a selective beta-2 adrenergic receptor agonist used primarily as a tocolytic agent to manage preterm labor. It works by relaxing uterine smooth muscle, thereby inhibiting contractions. In the Indian context, its use has declined significantly due to the availability of safer and more effective alternatives like nifedipine and atosiban, and due to its association with serious maternal cardiovascular and metabolic side effects. It is now considered a second-line agent.
Adult: **IV Infusion (Hospital Use Only):** Initial: 50-100 mcg/min, increased gradually by 50 mcg/min every 10-20 minutes until desired effect or unacceptable side effects occur. Usual effective dose: 150-350 mcg/min. Maximum recommended: 350 mcg/min. **Oral Maintenance (after IV):** 10 mg (one tablet) 30 minutes before stopping IV, then 10 mg every 2 hours for 24 hours, then 10-20 mg every 4-6 hours. Maximum oral dose: 120 mg/day. Duration of therapy should not exceed 48 hours.
Note: **IV Administration:** Must be diluted in a suitable IV fluid (e.g., 5% Dextrose or 0.9% Sodium Chloride). Use an infusion pump for precise control. Monitor maternal pulse, BP, respiratory rate, and fetal heart rate continuously. Monitor blood glucose and serum potassium levels. **Oral:** Can be taken with or without food. Administer with a full glass of water.
Ritodrine selectively stimulates beta-2 adrenergic receptors on uterine smooth muscle cells. This activation stimulates adenylate cyclase, increasing intracellular cyclic adenosine monophosphate (cAMP). Elevated cAMP levels activate protein kinase A, which phosphorylates key proteins, leading to a decrease in intracellular calcium concentration. The reduction in free calcium inhibits the activity of myosin light-chain kinase, resulting in uterine smooth muscle relaxation and suppression of contractions.
Pregnancy: **Category B (US FDA).** Used specifically in pregnancy for the management of preterm labor. Benefits must outweigh risks. Associated with maternal and fetal side effects. Not recommended for use beyond 48 hours.
Driving: May cause dizziness, nervousness, or tremors. Patients should be cautioned against driving or operating machinery until their response to the drug is known.
| Beta-blockers (e.g., Propranolol, Atenolol) | Antagonizes tocolytic effect of ritodrine; may worsen maternal bronchospasm in asthmatics. | Major |
| Corticosteroids (e.g., Betamethasone, Dexamethasone) | Increased risk of maternal pulmonary edema. Monitor fluid balance closely. | Major |
| Sympathomimetics (e.g., Salbutamol, Epinephrine) | Additive cardiovascular effects (tachycardia, hypertension). | Major |
| Digoxin | Increased risk of cardiac arrhythmias. | Moderate |
| Diuretics (e.g., Furosemide) | May potentiate hypokalemia. | Moderate |
| Insulin, Oral Hypoglycemics | Ritodrine causes hyperglycemia; may require adjustment of antidiabetic therapy. | Moderate |
| Magnesium Sulfate | Concurrent use may lead to profound neuromuscular blockade and cardiorespiratory depression. | Major |
| Ergot Alkaloids (e.g., Methylergometrine) | Direct pharmacological antagonism; avoid concurrent use. | Major |