普魯卡因胺
普魯卡因胺 (Procainamide) 是一種 **1A類抗心律不整藥物**，結構上與局部麻醉劑普魯卡因 (procaine) 相關。在獸醫學中，主要用於控制 **心室性心律不整**（如心室提早收縮 [VPCs] 和心室性心搏過速）以及某些 **心房性心搏過速** (SVTs)。 由於其對心房和心室心律不整具有廣泛的活性，當出現寬 QRS 波心搏過速且無法明確判定為心房性或心室性來源時，它通常被視為理想的第一線靜脈注射治療藥物。 > **臨床要點：** 與人類不同，犬隻是較差的乙醯化者，無法形成足量具活性的代謝物 N-乙醯普魯卡因胺 (NAPA)。因此，犬隻的治療藥物濃度監測應僅針對普魯卡因胺的濃度。
作用機制: Procainamide acts primarily as a **fast sodium channel blocker** (Class 1A), similar to quinidine. * **Phase 0 Blockade:** Slows the influx of sodium during Phase 0 depolarization of the cardiac action potential. * **→** Prolongs the refractory period in both the atria and ventricles. * **→** Decreases myocardial excitability and depresses automaticity and conduction velocity. * **Anticholinergic Effects:** Exhibits mild vagolytic properties which may cause slight increases in heart rate or unpredictable rate changes. * **ECG Effects:** Commonly causes widening of the QRS complex and prolongation of the PR and QT intervals.
各物種劑量
- Chronic management of SVTs · 3-8 mg/kg PO q6-8h · PO · q6-8h
- Chronic management of SVTs · 1-2 mg/kg slowly IV; 10-20 micrograms/kg/minute constant rate IV infusion · IV · Bolus then CRI
- Chronic management of SVTs · 7.5-20 mg/kg q 6-8h · PO · q6-8h
- Atrial fibrillation / Ventricular tachycardia · 1 mg/kg/min IV, not too exceed 20 mg/kg (20 minutes) total dose · IV · Once · 20 minutes max · Not as effective as quinidine for atrial fibrillation
- Atrial fibrillation / Ventricular tachycardia · 25-35 mg/kg PO q8h · PO · q8h
- V-Tach · 1 mg/kg/minute IV up to a total dose of 20 mg/kg; or 25-35 mg/kg PO q8h · IV/PO · Once or q8h
- Ventricular tachyarrhythmias · 2-4 mg/kg IV slowly (over two minutes) up to a total dose of 12-20 mg/kg until arrhythmia controlled and then a CRI may be started at 10-40 micrograms/kg/minute · IV · Intermittent boluses then CRI
- Ventricular tachyarrhythmias · 20-30 mg/kg PO q6-8h · PO · q6-8h · Previous recommendations of 8-20 mg/kg PO q6-8h are almost certainly too low
- Acute management of SVTs · 6-8 mg/kg IV over 3 minutes or 6-20 mg/kg IM · IV/IM · Once · After drugs have been used to slow AV nodal conduction (i.e., diltiazem)
給藥途徑
禁忌症
- Myasthenia gravis
- Hypersensitivity to procainamide, procaine, or chemically related drugs
- Systemic lupus erythematosus (SLE) in humans (unknown in dogs)
- Torsade de pointes
- 2nd or 3rd degree heart block (unless artificially paced)
- Doberman pinschers and boxers with dilated cardiomyopathy (relative - proarrhythmic risk)
- Dogs with subaortic stenosis (relative - proarrhythmic risk)
不良反應
- Anorexia
- Vomiting
- Diarrhea
- Weakness
- Hypotension (especially with rapid IV injection)
- Negative inotropism
- Widened QRS complex
- Prolonged QT interval
- AV block
- Multiform ventricular tachycardias
- Fevers
- Leukopenias
藥物相互作用
- Amiodarone · May increase procainamide levels; procainamide dose may need to be reduced
- Anticholinesterase agents (e.g., pyridostigmine, neostigmine) · Procainamide may antagonize effects in patients with myasthenia gravis
- Cimetidine · May increase procainamide levels
- Hypotensive drugs · Procainamide may enhance hypotensive effects
- Lidocaine · Toxic effects may be additive, and cardiac effects unpredictable
- Neuromuscular blocking agents · Procainamide may potentiate or prolong the neuromuscular blocking activity
- Quinidine · Toxic effects may be additive, and cardiac effects unpredictable
- Phenytoin · Toxic effects may be additive, and cardiac effects unpredictable
- Propranolol · Toxic effects may be additive, and cardiac effects unpredictable
- Ranitidine · May increase procainamide levels
- Trimethoprim · May increase procainamide levels
監測
- ECG (continuously with IV dosing)
- Blood pressure (during IV administration)
- Clinical signs of toxicity (GI signs, weakness)
- Serum drug levels (Trough levels for oral therapy. Note: Request lab to not run NAPA for dogs. Target range: 3-8 to 8-20 mcg/mL in dogs; 4-10 mcg/mL in horses)
過量
Clinical signs of overdosage can include **hypotension, lethargy, confusion, nausea, vomiting, and oliguria**. Cardiac signs may include widening of the QRS complex, junctional tachycardia, ventricular fibrillation, or intraventricular conduction delays. * **Oral Ingestion:** Emptying of the gut and charcoal administration may be beneficial to remove unabsorbed drug. * **Hypotension:** IV fluids, plus dopamine, phenylephrine, or norepinephrine could be considered. * **Cardiotoxicity:** A 1/6 molar intravenous infusion of sodium lactate may be used in an attempt to reduce cardiotoxic effects. * **Elimination:** Forced diuresis using fluids and diuretics along with reduction of urinary pH can enhance renal excretion. * **AV Block:** Temporary cardiac pacing may be necessary should severe AV block occur.
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