Usage
Terbutaline is prescribed for the prevention and reversal of bronchospasm in patients with asthma and other bronchopulmonary disorders such as bronchitis and emphysema where bronchospasm or reversible airway obstruction is a factor. It can also be used in the management of premature labor, but this is restricted due to significant risks. Its pharmacological classifications include bronchodilator, β₂-adrenergic agonist, and tocolytic (for premature labor, although use is now discouraged).
Terbutaline works by stimulating β₂-adrenergic receptors in the lungs, leading to the relaxation of bronchial smooth muscle and bronchodilation, making breathing easier. It also inhibits the release of bronchoconstricting substances from mast cells.
Alternate Names
Terbutaline Sulfate is the formal chemical name. Brand names include Bricanyl, Brethine, and Brethaire.
How It Works
Pharmacodynamics: Terbutaline acts as a β₂-adrenergic agonist. This means it binds to and activates β₂-adrenergic receptors, which are predominantly found in the lungs, uterus, and vascular smooth muscle. This binding triggers a cascade of intracellular events, leading to increased levels of cyclic adenosine monophosphate (cAMP). The rise in cAMP causes smooth muscle relaxation in the bronchi and uterus. In the lungs, this relaxation dilates the airways, relieving bronchospasm and improving airflow. In the uterus, it inhibits contractions.
Pharmacokinetics:
- Absorption: Terbutaline is readily absorbed after oral administration.
- Metabolism: It is primarily metabolized in the liver by conjugation.
- Elimination: Terbutaline is mainly excreted in the urine as metabolites, with some elimination in feces. The elimination half-life can range from 2.5 to 5 hours.
Mode of Action: Terbutaline exerts its bronchodilating effects primarily through β₂-receptor binding. It also interacts with G-proteins, leading to activation of adenylate cyclase and increased cAMP production. The rise in cAMP leads to smooth muscle relaxation. Terbutaline does not have significant effects on alpha-adrenergic receptors.
Elimination Pathways: Terbutaline is primarily eliminated through renal excretion as metabolites.
Dosage
Standard Dosage
Adults:
Oral: 2.5 mg to 5 mg taken three times per day, usually at approximately 6-hour intervals, only during waking hours. The maximum dose is 15 mg in a 24-hour period.
Children:
- Ages 12-15: 2.5 mg taken three times per day, approximately every 6 hours. The maximum dose is 7.5 mg in a 24-hour period.
- Ages 6-11: Inhalation Powder: 0.5 mg (1 inhalation) as needed, repeated doses 5 minutes apart. Maximum dose: 3 mg (6 inhalations) in 24 hours.
- Under 12 years (oral): 0.05 mg/kg three times daily initially; increase as needed, not to exceed 5 mg/day.
- Under 12 years (subcutaneous): 0.005–0.01 mg/kg (maximum 0.4 mg) every 15–20 minutes for three doses; then every 2–6 hours as needed.
Pediatric safety considerations: Use with caution, as children are more susceptible to side effects.
Special Cases:
- Elderly Patients: Start with a lower dose (2.5 mg three times daily) and monitor closely for adverse effects. Adjust dosage based on patient’s response and tolerance.
- Patients with Renal Impairment: Dose adjustment may be necessary. Consult specific guidelines for recommendations based on creatinine clearance.
- Patients with Hepatic Dysfunction: Start with a lower dose and monitor closely.
- Patients with Comorbid Conditions: Caution should be exercised in patients with diabetes, cardiovascular disease, hypertension, hyperthyroidism, and seizure disorders.
Clinical Use Cases
The use of terbutaline in clinical settings such as intubation, surgical procedures, mechanical ventilation, and the ICU should be approached with extreme caution due to potential cardiovascular side effects. Its use in these settings requires careful assessment of risks versus benefits. Terbutaline may be considered for acute bronchospasm in emergencies, with careful cardiac monitoring. It is not recommended for use in preventing premature labor due to potential risks to both mother and fetus.
Dosage Adjustments
Dosage modifications are necessary based on individual patient factors such as renal/hepatic function, metabolic disorders, and other concurrent medical conditions. Consult appropriate guidelines for specific recommendations.
Side Effects
Common Side Effects:
Nervousness, tremor, headache, tachycardia (fast heart rate), palpitations, dizziness, nausea, vomiting, anxiety, restlessness, lethargy, drowsiness, weakness, flushing, sweating, chest discomfort, and muscle cramps.
Rare but Serious Side Effects:
Severe allergic reactions (hives, difficulty breathing, swelling of the face or throat), worsening of bronchospasm (paradoxical bronchospasm), irregular heartbeat, chest pain, seizures, hyperglycemia, and hypokalemia.
Long-Term Effects:
Tolerance to the bronchodilating effects may develop with long-term use. Potential cardiovascular complications can occur with prolonged or excessive use.
Adverse Drug Reactions (ADR):
Clinically significant ADRs include cardiac arrhythmias, pulmonary edema, myocardial ischemia, and severe allergic reactions.
Contraindications
- Hypersensitivity to terbutaline or other sympathomimetic amines.
- Pre-existing conditions like tachyarrhythmias, severe coronary artery disease, and uncontrolled hypertension.
- Use beyond 72 hours for preterm labor.
- Oral administration for preterm labor.
Drug Interactions
- Beta-blockers: Can block the effects of terbutaline and cause severe bronchospasm.
- Diuretics (thiazides, loop diuretics): Can cause hypokalemia, increasing the risk of cardiac arrhythmias.
- Tricyclic antidepressants and MAO inhibitors: Can potentiate the cardiovascular effects of terbutaline.
- Other sympathomimetics: May increase the risk of cardiovascular side effects.
- General anesthetics: Can increase the risk of cardiac arrhythmias.
Pregnancy and Breastfeeding
Terbutaline is classified as Pregnancy Category C. It should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. Terbutaline is excreted in breast milk, and while the amount is generally low, it’s best to discuss with the patient the risks and benefits of using terbutaline while breastfeeding.
Drug Profile Summary
- Mechanism of Action: β₂-adrenergic agonist, relaxes bronchial smooth muscle.
- Side Effects: Tremor, nervousness, tachycardia, headache. Serious side effects include paradoxical bronchospasm, cardiac arrhythmias.
- Contraindications: Hypersensitivity to sympathomimetics, tachyarrhythmias.
- Drug Interactions: Beta-blockers, diuretics, tricyclic antidepressants, MAO inhibitors.
- Pregnancy & Breastfeeding: Use with caution, only if potential benefit outweighs risks.
- Dosage: Adults: 2.5-5 mg PO TID; Children: dose adjustments required (see above).
- Monitoring Parameters: Heart rate, blood pressure, respiratory rate, potassium levels, blood glucose (especially in diabetic patients).
Popular Combinations
Terbutaline is sometimes combined with corticosteroids for the treatment of asthma, but it’s becoming less common.
Precautions
- Pre-screening for underlying cardiovascular disease, diabetes, hyperthyroidism, and seizure disorders is essential.
- Pregnant Women: Avoid use for premature labor due to potentially severe maternal and fetal cardiovascular complications.
- Breastfeeding Mothers: The medication is excreted in breast milk and might affect the infant.
- Children & Elderly: Close monitoring is required due to increased sensitivity to side effects.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Terbutaline?
A: Adults: 2.5-5 mg orally three times daily. Children: dosage varies based on age and administration route. See detailed dosage guidelines above.
Q2: What are the most common side effects of Terbutaline?
A: The most common side effects include nervousness, tremor, headache, and tachycardia.
Q3: Can Terbutaline be used during pregnancy?
A: Terbutaline should be used during pregnancy only if the potential benefit outweighs the potential risk to the fetus, particularly due to the risk of cardiac side effects in both the mother and fetus.
Q4: How does Terbutaline work to treat asthma?
A: Terbutaline relaxes the bronchial smooth muscles, leading to bronchodilation and easing of breathing difficulties.
Q5: Are there any contraindications for Terbutaline use?
A: Yes. Contraindications include hypersensitivity to terbutaline or other sympathomimetic amines, certain heart conditions like tachyarrhythmias, and prolonged use for preterm labor.
Q6: What are the potential drug interactions with Terbutaline?
A: Significant drug interactions can occur with beta-blockers, certain diuretics, tricyclic antidepressants, and MAO inhibitors.
Q7: Is Terbutaline safe for breastfeeding mothers?
A: Terbutaline is excreted in breast milk. Although the amount is generally considered low, the potential risks to the infant should be discussed with the patient.
Q8: What should be monitored in patients taking Terbutaline?
A: Heart rate, blood pressure, respiratory rate, potassium levels, and blood glucose levels should be monitored, especially in diabetic patients.
Q9: Can Terbutaline be used to treat acute bronchospasm?
A: Yes, terbutaline can be used to treat acute bronchospasm, but with careful consideration of potential cardiac side effects. Close cardiac monitoring is necessary.
