Amiodarone
Amiodarone is a potent, broad-spectrum **Class III antiarrhythmic agent** used primarily for severe, refractory ventricular and supraventricular arrhythmias. Because of its complex pharmacokinetic profile and significant potential for toxicity, it is generally reserved for cases where conventional, less toxic therapies have failed. **Clinical Pearls:** * Structurally, amiodarone is an iodinated benzofuran derivative. A 200 mg tablet contains approximately 75 mg of iodine, which can impact thyroid function. * It is highly lipophilic, leading to extensive tissue distribution and accumulation in adipose tissue, which contributes to its exceptionally long and variable half-life. * In veterinary medicine, it is most notably used in Doberman Pinschers with occult dilated cardiomyopathy (DCM) presenting with rapid, wide-complex ventricular tachycardia or syncope. * Due to the high risk of adverse effects (including hepatotoxicity and thyroid dysfunction), rigorous monitoring is essential.
Mecanismo: 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.
Dosificación por especie
- 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.
Las dosis son una referencia clínica para médicos veterinarios. Confirme siempre con la información vigente del producto y el paciente individual.
Vías de administración
Contraindicaciones
- Hypersensitivity to amiodarone or iodine
- Severe sinus-node dysfunction
- Severe sinus bradycardia
- 2nd or 3rd degree AV block
- Bradycardial syncope
Efectos adversos
- 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)
Interacciones farmacológicas
- 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.
Monitoreo
- 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)
Sobredosis
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.
La referencia de fármacos de VetSheet está destinada a médicos veterinarios como apoyo a la decisión clínica; no sustituye el juicio profesional ni la información vigente del fabricante.