ピモベンダン
ピモベンダンは、**強心血管拡張薬（イノジレーター）**に分類される非常に有効な循環器薬であり、陽性変力作用（心収縮力の増強）と血管拡張作用の両方を併せ持ちます。 **主な臨床用途:** * **犬:** 主に**拡張型心筋症（DCM）**または**粘液腫性/変性性僧帽弁疾患（MMVD）**に続発するうっ血性心不全（CHF）の治療に使用されます。従来のACE阻害薬/フロセミド療法単独と比較して、生存期間と生活の質を大幅に改善します。ドーベルマンのDCMに対する第一選択薬と見なされており、ACVIMステージCおよびDの心不全管理の基礎となります。 * **猫:** 拘束型および拡張型心筋症に対して適応外使用されます。陽性変力作用があるため、肥大型心筋症（HCM）には通常禁忌です。 > **臨床のポイント:** モノグラフでは前臨床段階での使用に関する研究が進行中であると記されていますが、画期的なEPIC試験により、前臨床段階（ACVIMステージB2）のMMVDの犬における心不全の発症を遅らせるための標準治療としてピモベンダンが確立されています。
作用機序: Pimobendan exerts its dual **inodilator** effects through two distinct mechanisms: 1. **Positive Inotropy (Calcium Sensitization):** It increases the sensitivity of the cardiac myofilament **Troponin C** to intracellular calcium → enhances cardiac contractility. Unlike older inotropes (e.g., digoxin), it achieves this *without* increasing intracellular calcium levels → **no increase in myocardial oxygen consumption**. 2. **Vasodilation (PDE-III Inhibition):** It inhibits the enzyme **phosphodiesterase III (PDE-III)** in vascular smooth muscle → prevents the breakdown of cAMP → ↑ intracellular cAMP → smooth muscle relaxation → **mixed arterial and venous dilation**. This reduces both cardiac preload and afterload. Additionally, pimobendan possesses mild antithrombotic activity.
動物種別の用量
- Management of myocardial failure (DCM), especially if not associated with taurine deficiency · 1.25-1.5 mg/cat PO q12hrs · PO · q12h · Off-label use. Little information about clinical efficacy due to rarity of condition.
- Heart failure associated with systolic dysfunction (Off-label) · 0.1-0.3 mg/kg · PO · q12h · Lifelong · Not authorized (off-label). Pharmacokinetics may differ from dogs. Administer 1 hour before food.
- Management of the signs of mild, moderate or severe congestive heart failure due to AV valve insufficiency or dilated cardiomyopathy · 0.5 mg/kg total daily dose. Divide daily dose into two portions that are not necessarily equal (using whole and half tablets) and administer approximately 12 hours apart. · PO · Divided q12h
- Treatment of congestive heart failure secondary to myxomatous mitral valve disease (MMVD) · 0.4-0.6 mg/kg PO divided twice daily · PO · Divided twice daily
- Treatment of heart failure secondary to dilated cardiomyopathy or chronic mitral valve insufficiency · 0.25 mg/kg PO twice daily · PO · Twice daily
- General dosing · 0.2-0.6 mg/kg PO divided q12h · PO · Divided q12h
- Adjunctive drug for the emergency treatment of CHF (if not overtly critical and a strong positive oral inotrope is needed) · 0.1-0.3 mg/kg PO q12h · PO · q12h
- Adjunctive treatment of acute or chronic stage D heart failure (refractory to standard treatment) · 0.3 mg/kg PO to three times daily · PO · Up to TID · Outside of FDA-approved labeling; requires client consent.
投与経路
禁忌
- Hypersensitivity to pimobendan
- Hypertrophic cardiomyopathy (HCM)
- Aortic stenosis
- Any condition where augmentation of cardiac output is inappropriate for functional or anatomic reasons
- Any condition where augmentation of cardiac output via increased contractility is not possible anatomically or functionally
有害事象
- Poor appetite
- Lethargy
- Diarrhea
- Dyspnea
- Azotemia
- Weakness and ataxia
- Pleural effusion
- Syncope
- Cough
- Ascites
- Heart murmur
- Arrhythmias (atrial fibrillation, increased ventricular ectopic beats)
- Worsening mitral valve lesions (acute hemorrhages, endocardial papilloform hyperplasia) with chronic use
- Moderate positive chronotropic effect (tachycardia)
- Vomiting (dose-dependent)
- Reduced appetite or lethargy (rare)
薬物相互作用
- Verapamil · Calcium antagonist; attenuates pimobendan-induced increases in cardiac contractility.
- Propranolol · Beta-antagonist; attenuates pimobendan-induced increases in cardiac contractility.
- Diltiazem · Calcium channel blocker; assumed to potentially attenuate positive inotropic effects.
- Atenolol · Beta-blocker; assumed to potentially attenuate positive inotropic effects.
- Beta-blockers (e.g., atenolol, propranolol) · Attenuates the positive inotropic effects of pimobendan · moderate
- Calcium-channel blockers (e.g., verapamil, diltiazem) · Attenuates the positive inotropic effects of pimobendan · moderate
モニタリング
- ECG (rate and rhythm)
- Blood pressure
- Echocardiography (cardiac function and valve lesions)
- Clinical signs of heart failure (coughing, exercise intolerance)
- Resting respiratory rate (RRR) at home
- Heart rate and rhythm
- Respiratory rate and effort (Resting Respiratory Rate - RRR)
- Echocardiographic parameters (fractional shortening, left atrial/ventricular dimensions)
- Clinical signs of congestive heart failure
過量投与
Overdoses primarily manifest as cardiovascular signs. **Clinical Signs:** * Tachycardia (dose-dependent increases in heart rate) * Mild, non-clinical heart murmurs * Hypotension **Treatment:** * **Decontamination:** Induce emesis and administer activated charcoal if exposure was recent. * **Monitoring:** Continuously monitor heart rate, blood pressure, and ECG. * **Supportive Care:** Control hypotension with IV fluids and dopamine if necessary.
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