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# Bricanyl (Terbutaline)
## Overview
Terbutaline is a selective beta-2 adrenergic agonist. It acts as a bronchodilator by stimulating adenyl cyclase to increase cyclic AMP levels, causing bronchial smooth muscle relaxation. It also exerts a tocolytic effect by relaxing uterine smooth muscle.
## Primary Indications
* **Respiratory:** Relief of bronchospasm in patients with reversible obstructive airway disease (e.g., asthma, COPD).
* **Obstetrics:** Off-label use for the acute suppression of preterm labor (not FDA approved for long-term use due to maternal/fetal cardiovascular risk).
## Adult Dosing
* **Bronchospasm (Subcutaneous):** 0.25 mg injected into the lateral deltoid area. May repeat once after 15–30 minutes if needed. Do not exceed 0.5 mg in a 4-hour period.
* **Bronchospasm (Oral):** 2.5–5 mg every 6–8 hours. Maximum daily dose: 15 mg.
* **Preterm Labor (IV):** Highly variable; requires strict monitoring. Typically start at 2.5–5 mcg/min, increasing by 2.5 mcg/min every 20–30 minutes until contractions cease. Max: 25 mcg/min.
## Pediatric Dosing
* **Bronchospasm (Subcutaneous):** 0.005–0.01 mg/kg/dose (max 0.25 mg). May repeat every 15–20 minutes for two doses, then every 4–6 hours as needed.
* **Bronchospasm (Oral):** 0.05–0.15 mg/kg/dose every 8 hours. Max: 5 mg/dose.
## Dose Adjustments
* **Renal Impairment:** Reduce dose in patients with renal failure. No standardized guidelines exist; use clinical judgment and monitor for toxicity.
* **Hepatic Impairment:** Use with caution.
## Contraindications
* Known hypersensitivity to terbutaline or other sympathomimetic amines.
* Obstetric use: Known cardiac disease, chorioamnionitis, fetal demise, or conditions where prolongation of pregnancy is hazardous.
## Adverse Effects
* **Common:** Tachycardia, palpitations, fine tremors (skeletal muscle), nervousness, headache, dizziness, hypokalemia, hyperglycemia.
* **Serious:** Myocardial ischemia, pulmonary edema (common in prolonged IV tocolysis), arrhythmias, hypotension.
## Key Drug Interactions
* **Beta-blockers:** Antagonize the effect of terbutaline; avoid concomitant use.
* **Loop/Thiazide Diuretics:** Potential for worsening hypokalemia; monitor serum potassium.
* **MAO Inhibitors/TCAs:** May potentiate the pressor effects of beta-agonists on the vascular system.
## Monitoring
* **Cardiac:** Pulse, blood pressure, and ECG (if parenteral or in high-risk patients).
* **Respiratory:** Peak flow or FEV1, respiratory rate, and breath sounds.
* **Laboratory:** Serum potassium (especially with frequent dosing) and blood glucose.
* **Tocolysis:** Continuous fetal heart rate monitoring and maternal pulse; assess for shortness of breath or rales.
## Clinical Pearls
* **Systemic Exposure:** Oral bioavailability is low and variable (30–50%) due to extensive first-pass metabolism.
* **Tachyphylaxis:** Frequent or overly prolonged use may lead to a decrease in the bronchodilatory response.
* **FDA Warning:** The FDA has issued strong warnings regarding the use of oral or parenteral terbutaline for preterm labor due to serious maternal heart problems and death.
* **Local Protocols:** Hospital-specific policies for concentrations and infusion rates for tocolysis supersede general guidelines.
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**Educational Disclaimer:** This information is for educational purposes only. Drug information is subject to change. Always verify current prescribing information, institutional guidelines, and clinical protocols via trusted resources (e.g., Lexicomp, UpToDate, or the manufacturer’s package insert) before prescribing or administering medication.
