Ritodrine Hydrochloride is indicated for the treatment of uncomplicated premature labor.

Ritodrine hydrochloride is a selective β2-adrenergic receptor agonist. It acts by stimulating β2 receptors in the uterine smooth muscle, leading to relaxation of the uterus and a reduction in the frequency and intensity of uterine contractions. It decreases uterine myometrial contractility by increasing intracellular cyclic adenosine monophosphate (cAMP) levels and by influencing cell membrane mechanisms that regulate calcium movement. The increase in cAMP results in reduced intracellular calcium availability. Since calcium is essential for activation of smooth muscle contractile proteins, its reduction leads to inhibition of uterine contractions and promotes uterine relaxation.

By intravenous infusion: Initially 50 mcg/minute, increased gradually according to response by 50 mcg/minute every 10 minutes until contractions stop or maternal heart rate reaches 140 beats/minute; continue for 12–48 hours after contractions cease (usual rate 150–350 mcg/minute); maximum rate 350 mcg/minute.

Intramuscular injection: 10 mg every 3–8 hours, continued for 12–48 hours after contractions have ceased; then by mouth.

Oral maintenance treatment: One tablet (10 mg) may be given approximately 30 minutes before termination of intravenous therapy, repeated every 2 hours for 24 hours, followed by 10–20 mg every 4–6 hours; maximum oral dose 120 mg daily.

Risk of hypokalaemia may be increased when high doses of corticosteroids, diuretics (such as acetazolamide, loop diuretics, and thiazides), or theophylline are used together with high doses of ritodrine. Adequate time should be allowed before administering another sympathomimetic drug. β-adrenergic blockers inhibit the action of ritodrine and therefore should not be used together. When used with anesthetics during surgery, there may be an increased risk of hypotensive effects.

Ritodrine is contraindicated in patients with known hypersensitivity to the active ingredient or any excipients. It is also contraindicated in cardiac disease and in patients at significant risk of myocardial ischemia. It should be avoided in antepartum hemorrhage, intrauterine infection, intrauterine fetal death, placenta previa, abruptio placentae, threatened miscarriage, cord compression, eclampsia, and severe preeclampsia.

Common side effects include nausea, vomiting, flushing, sweating, tremor, hypokalaemia, tachycardia, palpitations, hypotension, uterine bleeding, pulmonary edema, chest pain or tightness, arrhythmias, and salivary gland enlargement. Prolonged use may lead to leukopenia, agranulocytosis, and liver function abnormalities including increased transaminases and hepatitis.

Ritodrine is classified as pregnancy category B. There are no adequate and well-controlled studies in women before 20 weeks of gestation; therefore, it should not be used before this period. From 20 weeks onward, studies have not shown increased risk of fetal abnormalities. However, possible fetal risks cannot be fully excluded, so it should be used only when clearly necessary. Reported neonatal effects include hypoglycemia and ileus, and in some cases hypocalcemia and hypotension when other beta-agonists were used. Use only when maternal benefit outweighs fetal risk.

Use with caution in suspected cardiac disease, hypertension, hyperthyroidism, hypokalaemia, diabetes mellitus, and mild to moderate preeclampsia. Blood pressure and pulse rate should be monitored, and overhydration should be avoided during therapy.

Overdose may cause tachycardia (maternal and fetal), palpitations, arrhythmias, hypotension, nervousness, tremor, nausea, and vomiting. If oral overdose occurs, gastric lavage or induced vomiting followed by activated charcoal may be used. In case of parenteral overdose, the drug should be stopped and a β-blocker may be administered as an antidote if necessary.

Drugs acting on the uterus

Keep out of reach of children. Store in a cool, dry place protected from light.