Ritodrine
Encyclopedia
Ritodrine is a tocolytic
Tocolytic
Tocolytics are medications used to suppress premature labor . They are given when delivery would result in premature birth...

 drug
Drug
A drug, broadly speaking, is any substance that, when absorbed into the body of a living organism, alters normal bodily function. There is no single, precise definition, as there are different meanings in drug control law, government regulations, medicine, and colloquial usage.In pharmacology, a...

, was used to stop premature labor. It is available in oral tablets or as an injection, and is typically used as the hydrochloride
Hydrochloride
In chemistry, hydrochlorides are salts resulting, or regarded as resulting, from the reaction of hydrochloric acid with an organic base . This is also known as muriate, derived from hydrochloric acid's other name: muriatic acid....

 salt, ritodrine hydrochloride. This drug has been removed from the market.

Mechanism

Ritodrine is a beta-2 adrenergic receptor
Beta-2 adrenergic receptor
The beta-2 adrenergic receptor , also known as ADRB2, is a beta-adrenergic receptor, and also denotes the human gene encoding it.-Gene:The gene is intronless...

 agonist
Agonist
An agonist is a chemical that binds to a receptor of a cell and triggers a response by that cell. Agonists often mimic the action of a naturally occurring substance...

 - a class of medication used for smooth muscle relaxation (other similar drugs are used in asthma or other pulmonary diseases such as salbutamol
Salbutamol
Salbutamol or albuterol is a short-acting β2-adrenergic receptor agonist used for the relief of bronchospasm in conditions such as asthma and chronic obstructive pulmonary disease. It is marketed as Ventolin among other brand names....

). Since ritodrine has a bulky N-substituent, it has high β2-selectivity. Also, the 4'-hydroxy on the benzene ring is important for activity as it is needed to form hydrogen bonds. However, the 4'-hydroxy makes it susceptible to metabolism by COMT. Since it is β2-selective it is used for premature labor.

Side effects and potential contraindications

Most side effects of beta-2 agonists result from their concurrent beta-1 activity, and include increase in heart rate, rise in systolic pressure, decrease in diastolic pressure, chest pain secondary to MI, and arrhythmia. Beta agonists may also cause fluid retention secondary to decrease in water clearance, which when added to the tachycardia
Tachycardia
Tachycardia comes from the Greek words tachys and kardia . Tachycardia typically refers to a heart rate that exceeds the normal range for a resting heart rate...

 and increased myocardial work, may result in cardiac failure. In addition, they increase gluconeogenesis
Gluconeogenesis
Gluconeogenesis is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as lactate, glycerol, and glucogenic amino acids....

 in the liver and muscle resulting in hyperglycemia, which increases insulin requirements in diabetic patients. The passage of beta-agonists through the placenta does occur and may be responsible for fetal tachycardia, as well as hypoglycemia or hyperglycemia at birth.

Patients with type 2 diabetes, high blood pressure or migraines should bring this to their doctor's attention before receiving care.

It has also been associated with post-partum hemorrhage.
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