Ritodrine has a beta-2-sympathicomimetic action.

Ritodrine is an uterine relaxant that is active after parenteral administration and for maintenance purposes after subsequent oral administration. It inhibits uterine contractions in frequency and intensity.

 

Studies carried out with 3H-labelled and unlabelled ritodrine in healthy volunteers reveal that regardless the route of administration, on average 90 % of the ritodrine dose is excreted in the urine.

After intravenous infusion of 150 micrograms ritodrine per minute for 1 hour, maximum plasma levels of approximately 40 ng/ml are quickly reached. One the infusion is stopped, the plasma level falls biexponentially with half-lives of 1.7 to 2.6 hours.

After intra-muscular injection of 10 mg ritodrine, peak plasma levels are 20-33 ng/ml with an elimination half-life of about 2 hours.

After oral administration of 10 mg ritodrine, peak plasma levels of 5-15 ng/ml are reached within 20-40 minutes. The effective elimination half-life is approximately 2 hours.

 

-Preterm labour.

-Prevention of preterm labour after operations.

-Acute foetal distress.

 

In general Ritodrine is contra-indicated in those conditions of the mother or foetus in which continuation of pregnancy is hazardous.

Specific contra-indications include:

- Antepartum haemorrhage due to any cause but particularly placenta previa and abruptio placentae.

- Eclampsia and severe pre-eclampsia.

- Intra-uterine foetal death.

- Chorioamnionitis.

- Maternal cardiac disorder.

- Known hypersensitivity to any component of the product.

- Hyperthyroidism.

- Uncontrolled hypertension.

- Any other condition which can endanger the cardiac function.

 

- Careful examination of patients with potential cardiac risks and cardiac abnormalities is recommended before deciding on ritodrine treatment.

- Because intravenous administration of ritodrine has been shown to elevate plasma insulin and glucose and to decrease potassium concentrations, glucose and electrolyte levels should be monitored. Special attention should be paid to biochemical variables when treating diabetic patients or those receiving potassium depleting diuretics.

- Less effects can be expected if the amniotic membranes are ruptured or the dilation of the cervix exceeds 4 cm.

 

The unwanted side-effects of Ritodrine are related to its beta-mimetic activity and high doses:

- Possibility of increase in maternal heart rate.

- Headache, erythema, nervousness, anxiety.

Most of the adverse signs and symptoms are reversible and dose related.

 

Caution should be taken when used concomitantly with:

- Corticosteroids.

- Other sympathomimetic amines.  

- Beta-adrenergic blocking drugs.

- Anaesthetics used in surgery.

 

Ritodrine is used to obtain uterine quiescence. As soon as the onset of preterm labour is diagnosed, the initial (parenteral) treatment with ritodrine should be started. Effective treatment of preterm labour is reflected by prolongation of pregnancy. Compared to preterm deliveries, the incidence of perineonatal morbidity and mortality is significantly lower in term deliveries.

The objective of ritodrine oral maintenance treatment is to prolong pregnancy and to prevent the relapse of preterm labour.

Intravenous infusion: To be started at the earliest onset of symptoms. Initial dose 0.05 mg/minute; increase by 0.05 mg/minute every 10-15 minutes until the desired result is obtained, unwanted side-effects occur or labour progresses despite treatment at the maximum dose; effective dose is usually between 0.15-0.35 mg/minute; maintain i.v. treatment: 12-48 hrs after ceased contractions.

Concentration of 0.3 mg/ml of the drug must be maintained (150 mg ritodrine hydrochloride solution in 500 ml fluid).

The diluent fluent should normally be 5% w/v dextrose solution, but not in the cases of diabetes mellitus.

Intramuscular injection: In case i.v. infusion cannot be provided 10 mg i.m. every 4-6 hours. Continue treatment for 12-48 hours after ceased contractions. The dosage should be increased or decreased according to the response or possible occurrence of unwanted side-effects.

After having reached uterine quiescence with i.v. or i.m. ritodrine administration and having maintained this situation for 12-48 hrs, oral therapy should be initiated 30-60 minutes before termination of parenteral therapy with:

Tablets: One or two 10 mg tablets every 2 – 6 hours.

The maximum daily dose is 120 mg. The usual daily dose: is 80 – 120 mg equally divided over the day.

The oral treatment may be continued as long as the physician considers it desirable to prolong pregnancy.

The objective of using ritodrine in such cases is to gain time necessary to arrive at definite decision how to deal best with the partus.

The initial intravenous treatment recommended for preterm labour should be followed. While the infusion is given, preparations should be made for the assisted delivery of the foetus.

If undesirable uterine motility occurs, the procedure recommended for the treatment of preterm labour should be adopted.

Guidance on infusion rates to achieve the required dose is given in the table below:

 

- UTOPRIN – Tablets: A blister pack of 20 tablets. Each tablet contains Ritodrine HCl 10 mg.

- UTOPRIN – Injection: A pack of 5 or 25 ampoules of 5 mL. Each ampoule (5 mL) contains Ritodrine HCl 50 mg.

 

- Store UTOPRIN – Tablets in a cool dry place, protected from light.

- Protect UTOPRIN Ampoules from light.