Terbutaline is a relatively selective β2-adrenergic bronchodilator that has little or no effect on alpha-adrenergic receptors. The drug has exerts a preferential effect on β2-adrenergic receptors but stimulates beta-adrenergic receptors less selectively than relatively selective β2-agonists. Terbutaline appears to have a greater stimulating effect on beta-receptors of the bronchial, vascular, and uterine smooth muscles (β2 receptors) than on the beta-receptors of the heart (β1 receptors). This drug relaxes smooth muscle and inhibits uterine contractions, but may also cause some cardiostimulatory effects and CNS stimulation.

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.

Terbutaline sulfate is indicated for the prevention and reversal of bronchospasm in patients 12 years of age and older with asthma and reversible bronchospasm associated with bronchitis and emphysema.

Use in bronchospasm: Terbutaline tablets and syrup have a duration of action of 7 to 8 hours. The minimum recommended dosage interval is therefore 7 hours.

Adults/Elderly:

• Tablets: During the first 1-2 weeks 2.5 mg (1 tablet) 3 times in a 24 hour period is recommended. The dose may then be increased to 5 mg (2 tablets) 3 times in 24 hours to achieve adequate bronchodilation.
• Syrup: The starting dose should be 2×5 ml spoonfuls (3 mg) 3 times in 24 hours. The dose may then be increased to 3×5 ml spoonfuls (4.5 mg) 3 times in 24 hours if necessary.

Children: 

• Tablets: 7-15 years, the starting dose should normally be 2.5 mg (1 tablet) 2 times in 24 hours. However, in some patients, the dose may need to be increased to 2.5 mg (1 tablet) 3 times in 24 hours.
• Syrup: 0.25 ml (0.075 mg)/kg body weight 3 times in a 24 hour period.

Patients with known hypersensitivity to Terbutaline.

The frequency of side-effects is low at the recommended doses. Side-effects which have been recorded such as tremor, headache, tonic cramp and palpitations are all characteristic of sympathomimetic amines. A few patients feel tense; this is also due to the effects on skeletal muscle and not to direct CNS stimulation. Whenever these side-effects have occurred the majority have usually been spontaneously reversible within the first week of treatment. Urticaria and exanthema may occur. In children sleep disturbances and disturbances of behavioural effects have been observed. Potentially serious hypokalaemia may result from β2-agonist therapy.

Possible symptoms: Headache, anxiety, tremor, tonic cramp, palpitations, arrhythmia. A fall in blood pressure sometimes occurs.

Treatment:

• Mild and moderate cases: Reduce the dose.
• Severe cases: Gastric lavage, administration of activated charcoal.

Care should be taken with patients suffering from myocardial insufficiency or thyrotoxicosis. Due to the hyperglycaemic effects of β2-stimulants, additional blood glucose measurements are initially recommended when Terbutaline therapy is commenced in diabetic patients. If a previously effective dosage regimen no longer gives the same symptomatic relief the patient should seek further medical advice, for reassessment of asthma therapy, as soon as possible. Potentially serious hypokalaemia may result from β2-agonist therapy. Particular caution is advised in severe asthma as this effect may be potentiated by concomitant treatment with xanthine derivatives, steroids, diuretics and by hypoxia. It is recommended that serum potassium levels are monitored in such situations. Due to the positive inotropic effect of β2-agonists, these drugs should not be used in patients with hypertophic cardiomyopathy.

Pregnancy & Lactation

Although no teratogenic effects have been observed in animals or in patients, Terbutaline should only be administered with caution during the first trimester of pregnancy. Terbutaline is secreted via breast milk, but effect on the infant is unlikely at therapeutic doses.