異丙腎上腺素
**異丙腎上腺素 (Isoproterenol)** 是一種強效的非選擇性 β-腎上腺素受體激動劑，主要用於獸醫急診醫學。 主要臨床特徵包括： * **心臟支持：** 用於治療嚴重的緩慢型心律不整，如完全性房室傳導阻滯或竇房結停搏，藉由增加心率和心肌收縮力來發揮作用。 * **支氣管擴張：** 過去曾用於急性支氣管收縮，但目前已大多被更具選擇性的 $\beta_2$ 激動劑（如特布他林或沙丁胺醇）取代，以避免心臟副作用。 * **休克/心臟衰竭：** 偶爾作為輔助治療，但由於其強烈的致心律不整潛力及引起心搏過速的傾向，使用受到限制。 **臨床要點：** 由於其強烈的心臟刺激特性，加上目前已有更安全、更具針對性的療法（例如用於房室傳導阻滯的心律調節器，或用於氣喘的選擇性支氣管擴張劑），異丙腎上腺素目前已較少使用。它的作用時間非常短，這意味著一旦停止輸注，副作用會迅速消退。
作用機制: **Isoproterenol** is a synthetic sympathomimetic amine that acts as a potent, non-selective agonist at both **$\beta_1$** and **$\beta_2$ adrenergic receptors**, with virtually no $\alpha$-adrenergic activity. **Mechanism Pathway:** Drug binds to **$\beta_1$ and $\beta_2$ receptors** → activates **Gs-proteins** → stimulates **adenylyl cyclase** → increases intracellular **cyclic-AMP (cAMP)** → activates **Protein Kinase A (PKA)**. * **Cardiac Effects ($\beta_1$):** Increased cAMP leads to increased intracellular calcium influx → **positive inotropy** (increased contractility) and **positive chronotropy** (increased heart rate and pacemaker discharge rate). * **Smooth Muscle Effects ($\beta_2$):** Increased cAMP inhibits myosin light-chain kinase (MLCK) → relaxation of bronchial smooth muscle (**bronchodilation**) and peripheral vasculature (**vasodilation**). * **Immunologic Effects:** Inhibits the antigen-mediated release of histamine and slow-releasing substance of anaphylaxis (SRS-A).
各物種劑量
- Sinoatrial arrest, sinus bradycardia, complete AV block · 0.4 mg in 250 mL D5W drip slowly to effect · IV · to effect
- Short-term bronchodilatation · Dilute 0.2 mg in 50 mL of saline and administer 0.4 micrograms/kg as an IV infusion, monitor heart rate continuously and discontinue when heart rate doubles. · IV · once · Effects may only last for an hour · ARCI UCGFS Class 2 Drug
- Sinoatrial arrest, sinus bradycardia, complete AV block · 0.4 mg in 250 mL D5W drip slowly to effect · IV · to effect
- Sinoatrial arrest, sinus bradycardia, complete AV block · Isuprel Glossets 5-10 mg · sublingual or rectal · q4-6h
- Sinoatrial arrest, sinus bradycardia, complete AV block · 0.04-0.08 micrograms/kg/min · IV · CRI · Infusion
- Sinoatrial arrest, sinus bradycardia, complete AV block · 0.1-0.2 mg · IM, SC · q4h
- Sinoatrial arrest, sinus bradycardia, complete AV block · 0.4 mg in 250 mL D5W slowly · IV · slowly
- Adjunctive treatment for bradycardia associated with calcium channel blocker overdose · Mix 0.4 mg in 250 mL of D5W and give via slow IV drip to effect. · IV · to effect · Alternative to atropine
劑量為持牌獸醫專業人員的臨床參考。請務必對照最新藥品說明書及個別病患確認。
給藥途徑
禁忌症
- Tachycardias or AV block caused by cardiac glycoside (digoxin) intoxication
- Ventricular arrhythmias that do not require increased inotropic activity
不良反應
- Tachycardia
- Ventricular arrhythmias (highly arrhythmogenic)
- Anxiety and excitability
- Tremors
- Headache
- Weakness
- Vomiting
藥物相互作用
- General Anesthetics (cyclopropane, halogenated hydrocarbons) · Increased risk of developing arrhythmias. Propranolol may be administered should these occur.
- Beta-Blockers · May antagonize isoproterenol's cardiac, bronchodilating, and vasodilating effects. Can be used to treat isoproterenol-induced tachycardia, but use with caution in bronchospastic disease.
- Digoxin (Digitalis glycosides) · Increased risk of arrhythmias.
- Oxytocic Agents · Hypertension may result if used concurrently.
- Other Sympathomimetic Agents (e.g., phenylpropanolamine) · Should not be administered concurrently as increased toxicity may result.
- Theophylline · May increase the risk for theophylline toxicity.
監測
- Cardiac rate and rhythm (ECG continuous monitoring highly recommended)
- Respiratory rate and auscultation (especially during anaphylaxis)
- Blood pressure
- Blood gases (if indicated and possible)
- Urine flow (if possible)
過量
High doses may cause an initial **hypertension**, followed by **hypotension**, as well as severe **tachycardias and other arrhythmias**. **Treatment:** * Halt or reduce the drug infusion (effects dissipate rapidly due to short half-life). * Provide supportive care. * If tachycardias persist, a **beta-blocker** could be considered for treatment, provided the patient does not have a bronchospastic disease.
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