Terbutaline

Oral
Acute bronchospasm
Adult: Initially, 2.5 mg or 3 mg tid, up to 5 mg tid as necessary. As modified-release tab: 5 mg or 7.5 mg bid.
Child: <12 yr Initially, 0.05 mg/kg/dose tid, increase gradually as required. Max: 5 mg/day; 12-15 yr 2.5 mg tid; >15 yr Same as adult dose.

Inhalation
Acute bronchospasm
Adult: As metered-dose powd inhaler: 250-500 mcg as required. Max: 2,000 mcg daily.

Parenteral
Severe bronchospasm
Adult: 250-500 mcg up to 4 times daily by SC, IM or IV inj, or by IV infusion as a soln containing 3-5 mcg/mL at a rate of 0.5-1 mL/min.
Child: 2-15 yr 0.01 mg/kg. Max: 0.3 mg/dose.
Reconstitution: Add 10 mL of terbutaline soln for inj to 40 mL of dextrose 5% if using a syringe pump or to 490 mL of dextrose 5% if syringe pump is not available.

Intravenous
Uncomplicated premature labour
Adult: To arrest labour between 22-37 wk of gestation: Initially, 5 mcg/min, w/ increments of 2.5 mcg/min at 20 min intervals until contractions stop. Max: 20 mcg/min. Continue for 1 hr after contractions have ceased, then decrease by 2.5 mcg/min every 20 min to lowest dose that maintains suppression. Max duration: 48 hr.
Reconstitution: Add 10 mL of terbutaline soln for inj to 40 mL of dextrose 5% if using a syringe pump or to 490 mL of dextrose 5% if syringe pump is not available.

Inhalation
Severe bronchospasm
Adult: As 1% nebuliser soln: 2.5-10 mg 2-4 times daily.
Child: <25 kg: 2-5 mg 2-4 times daily; ≥25 kg: 5 mg 2-4 times daily.

May be taken with or without food.

Parenteral: Prolonged (beyond 48-72 hr) or maintenance tocolysis, particularly in outpatient or home setting. PO: Acute or maintenance tocolysis.

Patient w/ thyrotoxicosis, HTN, DM, ketoacidosis, CV disorders (e.g. ischaemic heart disease), convulsive disorders, coronary insufficiency or associated arrhythmias. Childn. Pregnancy and lactation. Monitoring Parameters Monitor cardiorespiratory function, serum K and glucose levels; signs/symptoms of pulmonary oedema (when used in premature labour).

Tachycardia, nervousness, tremor, palpitations, dizziness, headache, nausea, vomiting, anxiety, restlessness, lethargy, drowsiness, weakness, flushes, sweating, chest discomfort, muscle cramps, tinnitus. Rarely, seizures, hypersensitivity vasculitis, elevated liver enzymes.
Potentially Fatal: Increased heart rate, transient hyperglycaemia, hypokalaemia, cardiac arrhythmias, pulmonary oedema, myocardial ischaemia.

Symptoms: Headache, anxiety, tremor, nausea, tonic cramps, palpitations, tachycardia, arrhythmia; hypotension, hypokalaemia, hyperglycaemia and lactic acidosis may occur. Management: Reduce dose in mild to moderate cases. In severe cases, perform necessary tests to determine acid-base balance, blood sugar and electrolyte levels. Monitor BP, heart rate and rhythm and correct metabolic changes. A cardioselective β-blocker (e.g. metoprolol) may be given for the treatment of arrhythmias but w/ caution.

Increased risk of haemorrhage and serious ventricular rhythm disorder w/ halogenated anaesth. May reduce the effect of anti-diabetic drugs. Increased risk of hypokalaemia w/ K-depleting agents (e.g. diuretics). Concomitant β-agonist and corticosteroid may result to pulmonary oedema. May partially or totally inhibit the effect of non-selective β-blockers.

Terbutaline stimulates intracellular adenyl cyclase, the enzyme that catalyses the conversion of ATP to cyclic-3?, 5?-adenosine monophosphate (cAMP) resulting in relaxation of bronchial smooth muscle and inhibition of release of mediators of immediate hypersensitivity from mast cells.
Onset: W/in 5 min (inhalation); 30-45 min (oral); 6-15 min (SC).
Duration: 6 hr (inhalation); 8 hr (oral).
Absorption: Variably absorbed from the GI tract (approx 30-50%); absorbed from the airways (<10%); well absorbed following SC admin. Bioavailability: Approx 14-15% (oral). Time to peak plasma concentration: 1-4 hr.
Distribution: Crosses the placenta and enters breast milk (trace amounts). Plasma protein binding: 25%.
Metabolism: Undergoes extensive first-pass metabolism via sulfate and some glucoronide conjugation in the liver and the gut wall.
Excretion: Via urine and faeces as inactive sulfate conjugate and unchanged drug. Terminal half-life: 16-20 hr.

Inhalation: Store between 20-25°C. Protect from light. Intravenous: Store between 20-25°C. Protect from light. Oral: Store between 20-25°C. Protect from light. Parenteral: Store between 20-25°C. Protect from light.

Drugs Acting on the Uterus / Antiasthmatic & COPD Preparations

R03AC03 - terbutaline ; Belongs to the class of adrenergic inhalants, selective beta-2-adrenoreceptor agonists. Used in the treatment of obstructive airway diseases.
R03CC03 - terbutaline ; Belongs to the class of adrenergics for systemic use, selective beta-2-adrenoreceptor agonists. Used in the treatment of obstructive airway diseases.