Disopyramide Phosphate
**Disopyramide phosphate** is a Class Ia (membrane-stabilizing) antiarrhythmic agent, structurally distinct but pharmacologically similar to quinidine and procainamide. * **Clinical Utility**: It is rarely used in veterinary medicine (primarily considered a 2nd or 3rd line agent for dogs) due to its short half-life and potent negative inotropic effects. * **Key Characteristics**: It reduces myocardial excitability and conduction velocity. Notably, it possesses significant anticholinergic (vagolytic) activity (150 mg of disopyramide is approximately equivalent to 0.09 mg of atropine), which heavily influences its side effect profile and contraindications. * **Cardiovascular Impact**: While it generally has minimal effects on resting heart rates or blood pressure, it can increase systemic peripheral resistance by up to 20% and significantly depress myocardial contractility.
Mecanismo: * Blocks **fast inward sodium (Na⁺) channels** → decreases the rate of phase 0 depolarization → slows conduction velocity through the atria and ventricles. * Inhibits **potassium (K⁺) channels** → prolongs the action potential duration and increases atrial and ventricular refractory times. * Decreases automaticity of ectopic atrial or ventricular pacemakers and shortens sinus node recovery time. * Exerts a direct **negative inotropic effect** on the myocardium, reducing cardiac contractility. * Possesses significant **anticholinergic (vagolytic) activity**, which can alter autonomic tone to the heart.
Dosificación por especie
- Antiarrhythmic (almost never used) · 7-30 mg/kg PO q4h · PO · q4h · Considered a 2nd or 3rd line agent.
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 the drug
- 2nd or 3rd degree AV block (unless a pacemaker is inserted)
- Cardiogenic shock
- Severe uncompensated or poorly compensated cardiac failure
- Hypotension
- Glaucoma (closed-angle)
- Urinary retention
- Myasthenia gravis
Efectos adversos
- Dry mouth, eyes, or nose
- Constipation
- Urinary hesitancy or retention
- Urinary frequency and urgency
- Edema
- Hypotension
- Dyspnea
- Syncope
- Conduction disturbances (e.g., AV block)
- Vomiting and diarrhea
- Intrahepatic cholestasis
- Hypoglycemia
- Fatigue and headache
- Muscle weakness and pain
- Prolonged QT interval (at 15 mg/kg q8h in dogs)
- Widened QRS complex (at doses >30 mg/kg in dogs)
Interacciones farmacológicas
- Anticholinergic drugs (atropine, glycopyrrolate) · Additive anticholinergic effects may be encountered.
- Cisapride · Additional prolongation of the QT interval.
- Macrolide antibiotics (erythromycin, clarithromycin) · Increased disopyramide levels; prolongation of QT interval may occur.
- Phenobarbital · May increase disopyramide's metabolism and reduce serum levels.
- Procainamide, Lidocaine · May be used concurrently, but widening of QRS and prolongation of QT interval may occur.
- Quinidine · May increase disopyramide levels; disopyramide may decrease quinidine levels.
- Rifampin · May increase disopyramide's metabolism and reduce serum levels.
- Verapamil · Because of additional negative inotropic effects, use of disopyramide within 48 hours of using verapamil is not recommended.
- Propranolol · May cause additive negative inotropic effects.
Monitoreo
- ECG (monitor for QT prolongation and QRS widening)
- Blood pressure
- Clinical signs of adverse effects (anticholinergic and cardiovascular)
- Liver function tests (if on chronic therapy)
- Serum drug levels (Therapeutic: 2-7 mcg/mL; Toxic: >9 mcg/mL)
Sobredosis
**Clinical signs of toxicity**: Anticholinergic effects, apnea, loss of consciousness, hypotension, cardiac conduction disturbances and arrhythmias, widening of the QRS complex and QT interval, bradycardia, congestive heart failure, seizures, asystole, and death. **Treatment**: * Initially consists of prompt gastric emptying, activated charcoal, and cathartics. * Follow with vigorous symptomatic therapy using cardiac glycosides, vasopressors, sympathomimetics, diuretics, mechanically assisted respiration, and endocardial pacing if necessary. * Disopyramide can be removed with hemodialysis.
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.