Ritodrine is a beta-2 adrenergic receptoragonist - a class of medication used for smooth muscle relaxation (other similar drugs are used in asthma or other pulmonary diseases such as salbutamol). 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 and increased myocardial work, may result in cardiac failure. In addition, they increase gluconeogenesis 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.