ジルチアゼム
ジルチアゼムは**非ジヒドロピリジン系カルシウムチャネル遮断薬**および**クラスIV抗不整脈薬**であり、獣医療では主に猫の上室性頻拍（SVT）、全身性高血圧、肺高血圧症、肥大型心筋症（HCM）の管理に使用されます。 * **心血管作用：** 主に房室結節の伝導を遅らせ、血管拡張を促進することで作用し、心房細動の心拍数コントロールに非常に有効です。 * **臨床的有用性：** 歴史的には猫のHCM治療の基本でしたが、近年この適応での使用は他の治療法に取って代わられつつあります。しかし、頻脈性不整脈の治療には依然として重要な薬剤です。 * **臨床のポイント：** 強力な末梢血管拡張薬であるジヒドロピリジン系（アムロジピンなど）とは異なり、ジルチアゼムは心刺激伝導系への影響が強いため、リズムコントロールには優れていますが、重度の全身性高血圧に対する降圧作用は弱いです。
作用機序: Diltiazem exerts its effects by binding to the alpha-1 subunit of **L-type voltage-gated calcium channels**. * **Mechanism:** Inhibits transmembrane influx of extracellular calcium ions → decreases intracellular calcium in myocardial cells and vascular smooth muscle. * **Cardiac Conduction:** Slows **AV node conduction** and prolongs refractory times (negative dromotropic effect). It rarely affects SA node conduction except in sick sinus syndrome. * **Vasodilation:** Relaxes vascular smooth muscle → dilates main systemic and coronary arteries → reduces total peripheral resistance, blood pressure, and cardiac afterload. * **Inotropy:** Can cause mild negative inotropic effects, though rarely of clinical significance compared to verapamil.
動物種別の用量
- Treatment of hypertrophic cardiomyopathy (Option A) · 7.5 mg (total dose) PO q8-12h; Long-acting forms: Cardizem CD Capsules: 10 mg/kg once daily. Dilacor XR Capsules: 15-30 mg total dose q12-24h. · PO · q8-24h · Some cats tolerate 60 mg daily, but vomiting may be a problem.
- Treatment of hypertrophic cardiomyopathy (Option B) · 1.75-2.5 mg/kg PO q8h or sustained release (Dilacor) dosed at 30 mg (total dose) PO q12h · PO · q8-12h
- Treatment of hypertrophic cardiomyopathy (Option C) · 7.5-15 mg (total dose) per cat PO q8h. Alternatively, the sustainedrelease products Cardizem CD at 45 mg (total dose) PO q24h or Dilacor XR at 30 mg (total dose; 1/2 of one of the 60 mg tablets found within the capsule) PO q12h can be used. · PO · q8-24h
- Treatment of hypertrophic cardiomyopathy (Option D) · If using standard release formulations: 1-2.5 mg/kg PO q8h; if using sustained release formations: 30-60 mg (total dose per cat) q24h. · PO · q8-24h · Also indicated for supraventricular arrhythmias.
- Treatment of hypertrophic cardiomyopathy (Option E) · Dilacor XR 30 mg/cat PO q24h. · PO · q24h · If cat has minimal tachycardia and a loud S4 gallop, many prefer using diltiazem (over a beta blocker).
- Emergency treatment of supraventricular tachyarrhythmias · Initially, 0.25 mg/kg IV bolus given over 2 minutes; subsequent 0.25 mg/kg boluses may be repeated at 15 minute intervals until conversion occurs or to a maximum (total) dose of 0.75 mg/kg. · IV · q15min
- Acute management of supraventricular tachyarrhythmias · 0.125-0.35 mg/kg IV · IV · As directed
- Chronic management of supraventricular tachyarrhythmias · 7.5 mg (per cat) PO q8h · PO · q8h · Used in combination with digoxin for patients with CHF unless cat has hypertrophic cardiomyopathy and atrial fib, then digoxin not used.
投与経路
禁忌
- Severe hypotension (<90 mm Hg systolic)
- Sick sinus syndrome (unless functioning pacemaker is in place)
- 2nd or 3rd degree AV block (unless functioning pacemaker is in place)
- Acute myocardial infarction
- Radiographically documented pulmonary congestion
- Hypersensitivity to diltiazem
- Second or third degree AV block
- Marked hypotension
- Sick sinus syndrome
- Acute or decompensated congestive heart failure (relative contraindication)
有害事象
- Dogs: Bradycardia (most prominent)
- Cats: Vomiting (especially with 60 mg sustained-release pellets)
- Lethargy
- Anorexia / GI distress
- Hypotension
- Heart block or rhythm disturbances
- CNS effects
- Skin rashes
- Elevations in liver enzymes
- Bradycardia (most common in dogs)
- Vomiting (most common in cats)
- AV block
薬物相互作用
- Anesthetics, General · May increase cardiac depressant effects of diltiazem.
- Benzodiazepines · Diltiazem may increase benzodiazepine levels.
- Beta-Blockers · May increase the likelihood of bradycardia, AV block, or CHF. Diltiazem may substantially increase the bioavailability of propranolol.
- Buspirone · Diltiazem may increase buspirone levels.
- Cisapride · Could potentially increase risk for increased QT intervals.
- Digoxin · Data conflicts regarding pharmacokinetic effects; diligent monitoring of digoxin serum concentrations is required. · moderate
- Cimetidine · May increase plasma diltiazem concentrations; increased monitoring warranted. · moderate
- Ranitidine · May affect diltiazem concentrations, but to a lesser extent than cimetidine.
- Cyclosporine · Diltiazem may increase cyclosporine serum concentrations; monitoring and dosage adjustments may be required.
- Rifampin · May decrease diltiazem levels.
- Quinidine · Diltiazem may increase quinidine serum concentrations; monitoring and dosage adjustments may be required.
- Beta-adrenergic blockers (e.g., propranolol) · Additive negative inotropic and chronotropic effects. Co-administration is not recommended. · major
モニタリング
- ECG / Heart rate
- Blood pressure
- Adverse effects (vomiting, lethargy)
- Heart rate and rhythm (ECG)
- Renal and hepatic function (periodically)
- Serum digoxin levels (if used concurrently)
過量投与
The oral LD50 in dogs is >50 mg/kg. * **Clinical Signs:** GI signs, heart block, severe bradycardia, hypotension, CNS depression, and heart failure. * **Treatment:** * Gut emptying protocols if recent ingestion. * **Bradycardia/AV Block:** Atropine. If unresponsive to vagal blockade, cautious use of isoproterenol. Fixed block may require temporary transvenous cardiac pacing. * **Hypotension/Heart Failure:** Inotropics (dobutamine, dopamine, isoproterenol) and pressors (norepinephrine). * **Antidote:** A slow intravenous calcium infusion (1 mL/10 kg body weight of 10% calcium gluconate) may be useful for severe acute toxicity.
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