プロカインアミド
プロカインアミドは、局所麻酔薬プロカインと構造的に関連する**クラス1A抗不整脈薬**です。獣医学では主に、**心室性頻脈性不整脈**（心室期外収縮 [VPC] や心室頻拍など）および特定の**上室性頻拍**（SVT）の管理に使用されます。 心房性および心室性不整脈の両方に対する幅広い活性スペクトルを持つため、広いQRS波を伴う頻拍が上室性か心室性か明確に特定できない場合、理想的な第一選択の静脈内治療薬と見なされることがよくあります。 > **臨床のポイント:** 人間とは異なり、犬はアセチル化能力が低く、活性代謝物であるN-アセチルプロカインアミド（NAPA）を十分に生成しません。したがって、犬の治療薬物モニタリングはプロカインアミド濃度のみに焦点を当てるべきです。
作用機序: 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.
動物種別の用量
- 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)
投与経路
禁忌
- 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)
有害事象
- 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
薬物相互作用
- 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
モニタリング
- 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)
過量投与
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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