アムロジピン
アムロジピンは**ジヒドロピリジン系カルシウムチャネル拮抗薬（CCB）**であり、獣医療では主に強力な**末梢動脈血管拡張薬**として使用されます。 - **猫の医療**：**猫の全身性高血圧**（慢性腎臓病、甲状腺機能亢進症、肥大型心筋症などに続発することが多い）の管理において**第一選択薬（ゴールドスタンダード）**とされています。猫では単独投与で高い有効性を示します。 - **犬の医療**：犬では、難治性うっ血性心不全（CHF）における後負荷軽減の補助薬として、または二次的な降圧薬として使用されます。犬に高用量で単独投与するとレニン・アンジオテンシン・アルドステロン系（RAAS）を活性化する可能性があるため、この作用を軽減するためにACE阻害薬（エナラプリルなど）と併用されることがよくあります。 - **臨床のポイント**：作用発現が比較的緩やかであるため、急性の低血圧クリーゼを防ぐのに役立ちますが、投薬を忘れると急激なリバウンド高血圧を引き起こす可能性があります。
作用機序: Amlodipine selectively inhibits the transmembrane influx of calcium ions into vascular smooth muscle and cardiac muscle by blocking **L-type voltage-gated calcium channels**. - **Vascular Smooth Muscle** → Relaxation and vasodilation → Significant reduction in **peripheral vascular resistance (afterload)** → Decreased systemic blood pressure. - It has a much higher affinity for vascular smooth muscle than cardiac muscle, meaning it produces profound vasodilation with minimal negative inotropic (contractility) or chronotropic (heart rate) effects at therapeutic doses. - **Cardiac Muscle** → Mildly depresses impulse formation (automaticity) and conduction velocity.
動物種別の用量
- Adjunctive therapy for refractory heart failure (advanced mitral valve degeneration as an afterload reducer) · 0.2-0.4 mg/kg PO twice daily. Initiate therapy at 0.1 mg/kg PO twice daily and up-titrate weekly while monitoring blood pressure. · PO · q12h · After ACE inhibitor maintenance therapy has been established.
- Arterial vasodilator for refractory CHF secondary to mitral regurgitation · 0.1 mg/kg q12-24h initially; titrate up as needed to 0.25 mg/kg PO q12-24h · PO · q12-24h · Monitor blood pressure.
- Systemic hypertension in dogs with chronic renal disease · 0.1-0.5 mg/kg PO once daily (q24h) · PO · q24h · Most often combined with an ACE inhibitor. May require weeks to months to achieve satisfactory control.
- Systemic hypertension (2nd step drug) · 0.1 mg/kg q24h; step up to 0.2 mg/kg q24h if needed · PO · q24h · Used after enalapril/benazepril. Each step added if after 1-2 weeks systolic BP > 160 mmHg.
- Systemic hypertension · 0.05-0.1 mg/kg (titrate upwards weekly as required, up to 0.5 mg/kg) · PO · q12-24h · Long-term · Monitor blood pressure regularly. Consider concurrent ACE inhibitor.
- Systemic hypertension (1st step drug) · 0.625 mg per cat q24h, if cat greater then 6 kg, 1.25 mg/cat q24h · PO · q24h · Add ACE inhibitor if proteinuric.
- Systemic hypertension · 0.625-1.25 mg (total dose) PO once daily · PO · q24h · Drug of choice; often successful as a single agent. Maximum effect seen within 7 days.
- Systemic hypertension · 0.625-1.25 mg/cat · PO · q24h (may increase slowly or increase frequency to q12h if necessary) · Long-term · Blood pressure monitoring is essential. Appears safe even with concurrent renal failure.
投与経路
禁忌
- Patients with cardiogenic shock
- Advanced aortic stenosis (relative contraindication)
- Use with caution in patients with heart failure (due to slight negative inotropic effects)
- Use with caution in patients with hepatic dysfunction
有害事象
- Cats: Infrequent azotemia, lethargy, hypokalemia, reflex tachycardia, weight loss
- Dogs: Gingival hyperplasia (with long-term use)
- Anorexia and hypotension (early in therapy)
薬物相互作用
- Diuretics · Concomitant use may cause additive hypotension. · moderate
- Beta-blockers · Concomitant use may cause additive hypotension. · moderate
- Vasodilators · Concomitant use may cause additive hypotension.
- Fentanyl · May cause hypotension if used concurrently.
- Grapefruit juice/powder · May alter bioavailability of amlodipine.
- Cimetidine · May impair hepatic metabolism of amlodipine, increasing circulating levels · moderate
- Cyclosporine · May impair hepatic metabolism of amlodipine, increasing circulating levels · moderate
- Ketoconazole · May impair hepatic metabolism of amlodipine, increasing circulating levels · moderate
- Itraconazole · May impair hepatic metabolism of amlodipine, increasing circulating levels · moderate
- Rifampin · CYP3A4 inducer; may reduce circulating amlodipine levels · moderate
- ACE inhibitors · Increased risk of hypotension when combined · moderate
モニタリング
- Systemic blood pressure (frequent monitoring during dose titration)
- Ophthalmic exam (to assess for hypertensive retinopathy/retinal detachment)
- Renal values and electrolytes (especially if combined with ACE inhibitors)
- Clinical signs of hypotension (lethargy, weakness)
過量投与
Overdoses pose a significant risk for **profound hypotension** and **reflex tachycardia** (though bradycardia is also possible). Common clinical signs in dogs and cats include lethargy and vomiting. **Treatment**: - When possible, massive overdoses should be managed with gut emptying (emesis/lavage) and activated charcoal. - Provide aggressive supportive treatment (IV fluids). - **Specific therapies** may include beta-agonists, intravenous lipid emulsion (ILE) therapy, and intravenous calcium to counteract the calcium channel blockade.
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