Terbutaline

Terbutaline is a synthetic, selective beta-2 adrenergic receptor agonist that acts as a bronchodilator. It is used to relieve bronchospasm in reversible obstructive airway diseases such as asthma and, in some regions, chronic obstructive pulmonary disease. It has also been used as a tocolytic to inhibit uterine contractions and delay preterm birth, though safety concerns have reduced its use for this indication.

Formulations include inhaled forms (metered-dose inhaler or nebulized solution) for quick relief of symptoms, and systemic forms such as oral tablets and subcutaneous or intravenous injections for obstetric use. Inhaled terbutaline provides local airway effects with fewer systemic effects, while systemic administration increases the potential for cardiovascular side effects.

Mechanism of action involves stimulation of beta-2 receptors on airway smooth muscle, increasing cyclic adenosine monophosphate (cAMP) and causing relaxation of bronchial smooth muscle. In the uterus, beta-2 activation also promotes relaxation of uterine smooth muscle, which underlies its historical use as a tocolytic. Terbutaline can also modulate mediator release from mast cells.

Common adverse effects include tachycardia, tremor, palpitations, nervousness, and headaches. Systemic use can cause hyperglycemia and hypokalemia and carries a higher risk of tachyarrhythmias and other cardiovascular events. Cautions include potential interactions with other sympathomimetics, monoamine oxidase inhibitors, and nonselective beta-blockers, and increased risk in patients with cardiovascular disease, diabetes, or hypertension. In pregnancy, tocolytic use is restricted to specialized medical supervision and current guidelines vary by region.