タダラフィル
タダラフィルは長時間作用型の**ホスホジエステラーゼ5 (PDE5) 阻害薬**であり、獣医療では主に犬の**肺動脈高血圧症 (PAH)** の管理に使用されます。 * **臨床のポイント**: シルデナフィルと比較して半減期が著しく長いため、1日1回または隔日投与が可能であり、飼い主のコンプライアンスが大きく向上します。 * 右心系の血圧が高い場合、従来の心不全治療薬（ピモベンダン、利尿薬、ACE阻害薬など）の補助療法として頻繁に使用されます。 * *注意*: 獣医療における臨床データや文献は現在非常に限られており、薬価が非常に高額になる場合があります。
作用機序: Tadalafil selectively inhibits **cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5)**. **Mechanism Pathway**: Endothelial stimulation → **Nitric Oxide (NO)** release → Activation of **guanylate cyclase** → Increased **cGMP** production. Normally, **PDE5** (found in pulmonary vascular smooth muscle, corpus cavernosum, and platelets) degrades cGMP. By inhibiting PDE5, tadalafil prevents this degradation. Increased intracellular **cGMP** → Decreased intracellular calcium in smooth muscle cells → **Relaxation of pulmonary vascular smooth muscle** → **Vasodilation** and significant reduction of pulmonary arterial pressure (PAP).
動物種別の用量
- Pulmonary arterial hypertension · 1 mg/kg PO q48h (every other day) · PO · q48h · Added to background treatment (furosemide, spironolactone, benazepril, dexamethasone, oxygen).
- Pulmonary arterial hypertension · 1 mg/kg PO once daily · PO · q24h
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
- Concurrent use of any form of organic nitrates (regularly or intermittently)
- Serious hypersensitivity to tadalafil
有害事象
- Cutaneous flushing of the inguinal region
- Gastrointestinal upset (dyspepsia, nausea)
- Decreased neutrophils and platelets (observed at 4X-18X human equivalent doses; reversible)
- Hypotension (especially if combined with other vasodilators)
- Myalgia or back pain (reported in humans)
- Headache or nasal congestion (reported in humans)
薬物相互作用
- Alpha-adrenergic blockers (e.g., phentolamine, phenothiazines, phenoxybenzamine) · May increase hypotensive effects
- Amlodipine · Potential to increase hypotensive effects
- Antihypertensive / Hypotensive drugs · Potentially could increase hypotensive effects
- Azole antifungals (ketoconazole, itraconazole) · May reduce tadalafil metabolism and increase AUC
- Cimetidine · May reduce tadalafil metabolism and increase AUC
- Erythromycin, Clarithromycin · May reduce tadalafil metabolism and increase AUC
- Nitrates (e.g., Nitroglycerin, Isosorbide) · Significant potentiation of vasodilatory effects; life-threatening hypotension possible
- Nitroprusside sodium · Significant potentiation of vasodilatory effects; life-threatening hypotension possible
- Phenobarbital · May decrease tadalafil concentrations
- Rifampin · May decrease tadalafil concentrations
モニタリング
- Clinical efficacy (improved syncope, cough, respiratory effort)
- Pulmonary artery pressure (via echocardiography)
- Systemic blood pressure
- Adverse effects (GI upset, flushing)
過量投与
Little information is available for veterinary species. In humans, single doses up to 500 mg and multiple daily doses up to 100 mg produced adverse reactions similar to those seen at lower doses. Overdoses in animals are expected to mirror the drug's adverse effect profile (e.g., severe hypotension, tachycardia, flushing). **Treat supportively** and contact an animal poison control center for guidance.
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。