| 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. |
| Pharmacodynamics |
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. |
| Absorption |
Approximately 30-50% if administered orally and well absorbed subcutaneously. |
| Volume of distribution |
Not Available |
| Protein binding |
Not Available |
| Metabolism |
Not Available |
| 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 |
| Half life |
5.5-5.9 hours |
| Clearance |
|
| 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 |
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