indication

For the prevention and reversal of bronchospasm in patients 12 years of age and older with reversible, obstructive airway disease, as well as symptomatic management of reversible bronchospasm associated with bronchitis and emphysema. Also used acute IV and sub-Q therapy in selected women to inhibit uterine contractions in preterm labor (tocolysis) and prolong gestation when beneficial.

pharmacology

Terbutaline is a relatively selective beta2-adrenergic bronchodilator that has little or no effect on alpha-adrenergic receptors. The drug has exerts a preferential effect on beta2-adrenergic receptors but stimulates beta-adrenergic receptors less selectively than relatively selective beta2-agonists. Terbutaline appears to have a greater stimulating effect on beta-receptors of the bronchial, vascular, and uterine smooth muscles (beta2 receptors) than on the beta-receptors of the heart (beta1 receptors). This drug relaxes smooth muscle and inhibits uterine contractions, but may also cause some cardiostimulatory effects and CNS stimulation.

mechanism of action

The pharmacologic effects of terbutaline are at least in part attributable to stimulation through beta-adrenergic receptors of intracellular adenyl cyclase, the enzyme that catalyzes the conversion of adenosine triphosphate (ATP) to cyclic- 3',5'- adenosine monophosphate (c-AMP). Increased c-AMP levels are associated with relaxation of bronchial smooth muscle and inhibition of release of mediators of immediate hypersensitivity from cells, especially from mast cells.

toxicity

Terbutaline Sulfate: Oral LD₅₀(rat) = 8.7 g/kg; Oral LD₅₀(mouse) = 205 mg/kg; Oral LD₅₀(dog) = 1.5 g/kg; IP LD₅₀(rat)= 220 mg/kg ; IP LD₅₀(mouse) = 130 mg/kg; Oral LD₅₀(rabbit) = >8 g/kg; IV LD₅₀(mouse) = 36 mg/kg; IV LD₅₀(dog) = 116 mg/kg; IV LD₅₀(rabbit) = 110 mg/kg

absorption

Approximately 30-50% if administered orally and well absorbed subcutaneously.

half life

5.5-5.9 hours

route of elimination

About 90% of the drug was excreted in the urine at 96 hours after subcutaneous administration, with about 60% of this being unchanged drug. It appears that the sulfate conjugate is a major metabolite of terbutaline and urinary excretion is the primary route of elimination

drug interactions

Acebutolol: Antagonism

Alseroxylon: Increased arterial pressure

Amitriptyline: The tricyclic antidepressant, amitriptyline, increases the sympathomimetic effect of terbutaline.

Amoxapine: The tricyclic antidepressant, amoxapine, increases the sympathomimetic effect of terbutaline.

Atenolol: Antagonism

Betaxolol: Beta-Blockers (Beta1 Selective) like betaxolol may diminish the bronchodilatory effect of Beta2-Agonists like terbutaline. Therapy should be monitored.

Bevantolol: Antagonism

Bisoprolol: Antagonism

Carteolol: Antagonism

Carvedilol: Antagonism

Clomipramine: The tricyclic antidepressant, clomipramine, increases the sympathomimetic effect of terbutaline.

Deserpidine: Increased arterial pressure

Desipramine: The tricyclic antidepressant, desipramine, increases the sympathomimetic effect of terbutaline.

Doxepin: The tricyclic antidepressant, doxepin, increases the sympathomimetic effect of terbutaline.

Esmolol: Antagonism

Imipramine: The tricyclic antidepressant, imipramine, increases the sympathomimetic effect of terbutaline.

Isocarboxazid: Increased arterial pressure

Labetalol: Antagonism

Linezolid: Possible increase of arterial pressure

Methyldopa: Increased arterial pressure

Metoprolol: Antagonism

Midodrine: Increased arterial pressure

Moclobemide: Moclobemide increases the sympathomimetic effect of terbutaline.

Nadolol: Antagonism

Nortriptyline: The tricyclic antidepressant, nortriptyline, increases the sympathomimetic effect of terbutaline.

Oxprenolol: Antagonism

Pargyline: Increased arterial pressure

Penbutolol: Antagonism

Phenelzine: Increased arterial pressure

Pindolol: Antagonism

Practolol: Antagonism

Propranolol: Antagonism

Protriptyline: The tricyclic antidepressant, protriptyline, increases the sympathomimetic effect of terbutaline.

Rasagiline: Increased arterial pressure

Reserpine: Increased arterial pressure

Sotalol: Antagonism

Timolol: Antagonism

Tranylcypromine: Increased arterial pressure

Trimipramine: The tricyclic antidepressant, trimipramine, increases the sympathomimetic effect of terbutaline.