ベラパミル
ベラパミルは**非ジヒドロピリジン系カルシウムチャネル遮断薬**であり、**クラスIV抗不整脈薬**です。 血管平滑筋に作用して血管拡張を引き起こすジヒドロピリジン系カルシウムチャネル遮断薬（アムロジピンなど）とは異なり、ベラパミルは心臓の刺激伝導系、特に房室結節（AV結節）に強い影響を与えます。 **主な臨床用途:** * 獣医療では主に、犬および猫の**上室性頻拍（SVT）**の管理に使用されます。 * 心房粗動または心房細動における心室拍動数のコントロールに使用されることがあります。 * **臨床のポイント:** ベラパミルは**P-糖タンパク質（P-gp）**の阻害薬として知られています。このメカニズムにより、抗てんかん薬が中枢神経系から排出されるのを防ぐ目的で、難治性てんかんの補助治療薬として研究されています。
作用機序: Verapamil exerts its effects by blocking the transmembrane influx of extracellular calcium ions through **L-type voltage-gated calcium channels** in myocardial cells and vascular smooth muscle cells. * **Cardiac Conduction (Primary Effect):** Blocks calcium channels in the SA and AV nodes → **decreases AV node conduction velocity** and increases the effective refractory period → slows ventricular response rate in supraventricular arrhythmias. * **Myocardial Contractility:** Exhibits a **negative inotropic effect** (decreases heart muscle contractility). * **Vascular Smooth Muscle:** Inhibits contractile mechanisms → causes vasodilation and decreases peripheral vascular resistance (though less potently than amlodipine). * **Neurological:** Inhibits **P-glycoprotein (MDR1/ABCB1)** at the blood-brain barrier → reduces the efflux of certain substrate drugs back into the systemic circulation.
動物種別の用量
- Supraventricular tachycardia · Initial dose of 0.025 mg/kg IV slowly, can repeat every 5 minutes up to a total dose of 0.15-0.2 mg/kg; Oral Dose: 0.5-1 mg/kg PO q8h · IV/PO · q8h (for PO)
- Supraventricular tachyarrhythmias · 0.5-1 mg/kg · PO · q8h
- Supraventricular tachyarrhythmias (Acute) · 0.025 mg/kg · IV · once · over 5 minutes · Administer slowly with ECG monitoring. Up to 3 repeat IV administrations q5min if necessary.
- To control ventricular rate in atrial fibrillation · 0.025-0.05 mg/kg IV q 30 minutes; give less than 0.2 mg/kg total dose · IV · q 30 minutes · ARCI UCGFS CLASS 4 DRUG
- Cardiovascular disease · 0.25-0.5 mg (total dose per hamster) SC · SC · Hamsters
- Cardiovascular disease · 8-16 mg/kg PO + 0.5-2 mg/kg SC once daily (q24h) · PO/SC · q24h · Rabbits
- Supraventricular tachycardia · Initial dose of 0.05 mg/kg IV slowly, can repeat every 5 minutes up to a total dose of 0.15-0.2 mg/kg; Oral Dose: 0.5-2 mg/kg PO q8h · IV/PO · q8h (for PO)
- Treatment of hypertension · 1-5 mg/kg PO q8h · PO · q8h
投与経路
禁忌
- Cardiogenic shock
- Severe CHF (unless secondary to a supraventricular tachycardia amenable to verapamil)
- Hypotension (<90 mmHg systolic)
- Sick sinus syndrome
- 2nd or 3rd degree AV block
- Digoxin intoxication
- Hypersensitivity to verapamil
- Recent use (within a few hours) of IV beta-adrenergic blockers
- Hypotension
- Left ventricular dysfunction
- Heart failure
有害事象
- Hypotension
- Bradycardia
- Tachycardia
- Exacerbation of congestive heart failure (CHF)
- Peripheral edema
- AV block
- Pulmonary edema
- Nausea
- Constipation
- Dizziness
- Headache
- Fatigue
- Precipitation or exacerbation of congestive heart failure
薬物相互作用
- ACE Inhibitors · May cause additive hypotensive effects
- Alpha-Adrenergic Blockers (e.g., prazosin) · May cause additive hypotensive effects
- Beta-Adrenergic Blockers (e.g., propranolol) · May cause additive negative cardiac inotrope and chronotrope effects; IV combination is contraindicated
- Doxorubicin · Verapamil may increase doxorubicin concentrations
- COPP Chemotherapy · May decrease oral absorption of verapamil
- Cyclosporine · Verapamil may increase cyclosporine levels
- Dantrolene · Cardiovascular collapse reported in animals when used with verapamil
- Digoxin · Verapamil may increase blood levels of digoxin; monitoring recommended · major
- Disopyramide · May cause additive effects and impair left ventricular function; concurrent use within 24-48 hours not recommended
- Diuretics · May cause additive hypotensive effects
- Erythromycin, Clarithromycin · May increase verapamil levels
- Flecainide · Possible additive effects; concurrent use is to be avoided in humans
- Neuromuscular Blockers · Effects of nondepolarizing muscle relaxants may be enhanced by verapamil
モニタリング
- ECG
- Clinical signs of toxicity (hypotension, bradycardia, edema)
- Blood pressure (especially during acute IV therapy)
- Serum concentration (if efficacy or toxicity warrant; 100-300 ng/mL is considered therapeutic)
- ECG (especially during IV administration)
- Blood pressure
- Heart rate and rhythm
- Liver function (in patients with hepatic disease)
過量投与
**Clinical Signs of Overdose:** Bradycardia, hypotension, hyperglycemia, junctional rhythms, and 2nd or 3rd degree AV block. **Treatment:** * **Decontamination:** If secondary to recent oral ingestion, consider gut emptying and activated charcoal administration. * **Supportive Care:** Vigorously monitor cardiac and respiratory function. * **Negative Inotropy:** Intravenous calcium salts (1 mL of 10% solution per 10 kg of body weight) may treat negative inotropic signs, but may not adequately resolve heart block. * **Hypotension:** Fluid therapy and pressor agents (e.g., dopamine, norepinephrine) may be utilized. * **AV Block / Bradycardia:** Treat with isoproterenol, norepinephrine, atropine, or cardiac pacing. * **Rapid Ventricular Rate:** Patients developing rapid ventricular rate due to antegrade conduction in flutter/fibrillation with WPW syndrome have been treated with D.C. cardioversion, lidocaine, or procainamide.
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