リン酸ジソピラミド
**リン酸ジソピラミド**は、クラスIa（膜安定化）抗不整脈薬であり、構造的にはキニジンやプロカインアミドと異なりますが、薬理学的には類似しています。 * **臨床的有用性**：半減期が短く、強力な陰性変力作用があるため、獣医療ではほとんど使用されません（主に犬の第2または第3選択薬と見なされます）。 * **主な特徴**：心筋の興奮性と伝導速度を低下させます。特に、顕著な抗コリン（迷走神経遮断）作用（ジソピラミド150 mgはアトロピン約0.09 mgに相当）を有しており、これが副作用や禁忌に大きく影響します。 * **心血管系への影響**：通常、安静時の心拍数や血圧への影響は最小限ですが、全身の末梢血管抵抗を最大20%増加させ、心筋収縮力を著しく低下させる可能性があります。
作用機序: * 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.
動物種別の用量
- Antiarrhythmic (almost never used) · 7-30 mg/kg PO q4h · PO · q4h · Considered a 2nd or 3rd line agent.
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 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
有害事象
- 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)
薬物相互作用
- 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.
モニタリング
- 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)
過量投与
**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.
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。