Ritodrine is a tocolytic drug, used to stop premature labor. It was available in oral tablets or as an injection and was typically used as the hydrochloride salt, ritodrine hydrochloride. Ritodrine is a beta-2 adrenergic receptor agonist - a class of medication used for smooth muscle relaxation. 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. 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.
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