アミオダロン
アミオダロンは、重度で難治性の心室性および上室性不整脈に主に使用される、強力で広域スペクトルの**クラスIII抗不整脈薬**です。 複雑な薬物動態プロファイルと重大な毒性の可能性があるため、通常は従来の毒性の低い治療法が効果を示さない場合にのみ使用されます。 **臨床のポイント：** * 構造的には、アミオダロンはヨウ素化ベンゾフラン誘導体です。200mgの錠剤には約75mgのヨウ素が含まれており、甲状腺機能に影響を与える可能性があります。 * 脂溶性が非常に高く、組織に広く分布し脂肪組織に蓄積するため、半衰期が非常に長く変動しやすい特徴があります。 * 獣医学においては、特に潜在性拡張型心筋症（DCM）を患い、急速な幅広い心室頻拍や失神を呈するドーベルマン・ピンシャーに最もよく使用されます。 * 副作用（肝毒性や甲状腺機能障害など）のリスクが高いため、厳密なモニタリングが不可欠です。
作用機序: Amiodarone is uniquely versatile, possessing properties of all four Vaughan-Williams antiarrhythmic classes, though it is primarily classified as a **Class III** agent. * **Class III (Primary):** Blocks **potassium (K+) channels** → prolongs phase 3 repolarization, action-potential duration (APD), and the effective refractory period (ERP) in myocardial cells. * **Class I:** Blocks **fast sodium (Na+) channels** → slows conduction velocity. * **Class II:** Non-competitively blocks **beta-adrenergic receptors** → provides sympatholytic effects, reducing heart rate. * **Class IV:** Weakly blocks **calcium (Ca2+) channels** → slows AV node conduction and suppresses automaticity. It is metabolized in the liver to its active metabolite, **desethylamiodarone**, which also contributes significantly to its antiarrhythmic effects.
動物種別の用量
- For atrial fibrillation or ventricular arrhythmias primarily in ambulatory patients · 8-10 mg/kg PO every 12 hours · PO · q12h · Use caution if patient has bradycardia, AV blocks, or thyroid disorders.
- For ventricular arrhythmias secondary to occult cardiomyopathy in Doberman pinschers · 10 mg/kg PO twice daily for one week and then 8 mg/kg PO once daily. After 6 months reduce to 5 mg/kg PO once daily. · PO · q12h then q24h · Long-term · For severe V-Tach, mexiletine is added at 5-8 mg/kg three times daily for one week. Once efficacy confirmed, patient weaned off mexiletine.
- For ventricular tachycardia when other first line drugs (Class I antiarrhythmics ± beta-blockers) are ineffective · 10 mg/kg PO q12h for one week and then 5 mg/kg PO q12h for maintenance. · PO · q12h · Long-term
- For SVTs or Vtach · 10-20 mg/kg PO once daily (q24h) loading for 5-7 days; 5-10 mg/kg PO once daily thereafter. · PO · q24h · Long-term
- Ventricular and supraventricular arrhythmias, atrial fibrillation, ventricular pre-excitation syndromes · Dose not specified in monograph · PO/IV · Not specified · Not specified · Use as an IV infusion for recent onset atrial fibrillation has variable efficacy for restoring sinus rhythm but a high frequency of severe adverse effects.
- For conversion of atrial fibrillation or ventricular tachycardia · 5 mg/kg/hr for one hour, followed by 0.83 mg/kg/hr for 23 hours and then 1.9 mg/kg/hour for the following 30 hours. · IV · CRI · Up to 54 hours · Infusion was discontinued when conversion occurred or when any side effects were noted. Regimen should be further adapted based upon PK/PD studies.
用量は獣医療従事者向けの臨床リファレンスです。必ず最新の添付文書と個々の患者で確認してください。
投与経路
禁忌
- Hypersensitivity to amiodarone or iodine
- Severe sinus-node dysfunction
- Severe sinus bradycardia
- 2nd or 3rd degree AV block
- Bradycardial syncope
有害事象
- Vomiting
- Anorexia
- Hepatopathy (elevated liver enzymes, bilirubinemia)
- Bradycardia
- Neutropenia
- Thrombocytopenia
- Positive Coombs' test
- Corneal deposits
- Injection site pain (IV)
- Facial pruritus and hyperemia (IV)
- Hind limb weakness (horses)
- Diarrhea (horses)
薬物相互作用
- Warfarin (Anticoagulants) · Significantly increases serum levels and/or pharmacologic/toxic effects of the anticoagulant.
- Digoxin · Significantly increases serum levels and/or toxic effects of digoxin. · major
- Cyclosporine · Increases cyclosporine levels; may increase creatinine.
- Lidocaine · Significantly increases serum levels and/or toxic effects of lidocaine. · moderate
- Methotrexate · Significantly increases serum levels and/or toxic effects with prolonged amiodarone administration. · major
- Phenytoin · Significantly increases serum levels and/or toxic effects of phenytoin.
- Procainamide · Significantly increases serum levels and/or toxic effects of procainamide.
- Quinidine · Significantly increases serum levels and/or toxic effects of quinidine.
- Azole Antifungals (ketoconazole, itraconazole) · Additive effects on QTc interval; possible serious arrhythmias.
- Cisapride · Additive effects on QTc interval; possible serious arrhythmias.
- Disopyramide · Additive effects on QTc interval; possible serious arrhythmias.
- Dolasetron · Additive effects on QTc interval; possible serious arrhythmias.
モニタリング
- ECG (for antiarrhythmic efficacy and proarrhythmic effects)
- Gastrointestinal signs (anorexia, vomiting)
- CBC (for neutropenia, thrombocytopenia)
- Serial liver enzymes and bilirubin (baseline and routine monitoring)
- Thyroid function tests
- Blood pressure
- Pulmonary radiographs (if clinical signs such as dyspnea or cough occur)
過量投与
Clinical overdosage experience is limited. **Expected Signs:** * Hypotension * Bradycardia * Cardiogenic shock * AV block * Hepatotoxicity **Treatment:** * Therapy is primarily **supportive**. * Bradycardia may be managed with a pacemaker or beta-1 agonists (e.g., isoproterenol). * Hypotension may be managed with positive inotropic agents or vasopressors. * *Note:* Neither amiodarone nor its active metabolite are dialyzable.
VetSheet の薬剤リファレンスは、獣医療従事者向けの臨床意思決定支援を目的としており、専門的判断やメーカーの最新添付文書に代わるものではありません。