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 due to the availability of safer alternatives like nifedipine and atosiban, but it remains a part of the therapeutic arsenal, particularly in specific hospital settings. It is administered via intravenous infusion or orally for maintenance therapy.
Adult: For preterm labor: IV infusion: Initial 50-100 mcg/min, increased gradually by 50 mcg/min every 10-20 minutes until contractions cease or unacceptable side effects occur. Usual effective dose: 150-350 mcg/min. Maximum recommended IV dose: 350 mcg/min. Oral maintenance: After successful IV tocolysis, 10 mg (one 10mg tablet) orally 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. NOTE: The 40mg strength is typically used for oral maintenance therapy, often as a sustained-release formulation to allow less frequent dosing (e.g., 40mg every 8 hours).
Note: IV: Must be diluted in appropriate IV fluid (e.g., 0.9% NaCl, 5% Dextrose). Administer via controlled infusion pump. Monitor maternal pulse, BP, and fetal heart rate continuously. Oral: Can be taken with or without food. Swallow tablet whole; do not crush or chew sustained-release formulations. Maintain adequate hydration.
Ritodrine selectively stimulates beta-2 adrenergic receptors on uterine smooth muscle cells. This activation increases intracellular cyclic adenosine monophosphate (cAMP) levels via adenylate cyclase. Elevated cAMP activates 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, preventing the interaction of actin and myosin, resulting in uterine muscle relaxation and suppression of contractions.
Pregnancy: US FDA Category B. Used specifically during pregnancy for the treatment of preterm labor. Benefits must outweigh risks. Monitor mother and fetus closely for adverse effects.
Driving: May cause dizziness, nervousness, or tremor. Patients should be cautioned about operating machinery or driving until they know how the drug affects them.
| Beta-blockers (e.g., Propranolol, Atenolol) | Antagonizes tocolytic effect of ritodrine; may cause severe hypertension. | Major |
| Corticosteroids (e.g., Betamethasone, Dexamethasone) | Increased risk of pulmonary edema and hyperglycemia. | Major |
| Sympathomimetics (e.g., Salbutamol, Terbutaline) | Additive cardiovascular effects (tachycardia, arrhythmias). | Major |
| Diuretics (e.g., Furosemide) | Increased risk of hypokalemia. | Moderate |
| Digoxin | Increased risk of cardiac arrhythmias. | Moderate |
| Atropine | Potentiates tachycardia. | Moderate |
| Ergot Alkaloids (e.g., Methylergometrine) | Opposing pharmacological effects; can cause severe hypertension. | Major |
| General Anesthetics (Halothane) | Increased risk of ventricular arrhythmias. | Major |