他達拉非
他達拉非 (Tadalafil) 是一種長效的**第五型磷酸二酯酶 (PDE5) 抑制劑**，在獸醫學中主要用於控制犬隻的**肺動脈高壓 (PAH)**。 * **臨床重點**：與西地那非 (Sildenafil) 相比，他達拉非的半衰期顯著較長，允許每日一次或每兩日一次給藥，大幅提高飼主的順從性。 * 當右心壓力持續升高時，常作為傳統心臟衰竭藥物（如匹莫苯、利尿劑、ACE抑制劑）的輔助療法。 * *注意*：目前在獸醫物種中的臨床數據和已發表的文獻非常有限，且藥費可能相當昂貴。
作用機制: 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).
各物種劑量
- 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
劑量為持牌獸醫專業人員的臨床參考。請務必對照最新藥品說明書及個別病患確認。
給藥途徑
禁忌症
- Concurrent use of any form of organic nitrates (regularly or intermittently)
- Serious hypersensitivity to tadalafil
不良反應
- 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)
藥物相互作用
- 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
監測
- Clinical efficacy (improved syncope, cough, respiratory effort)
- Pulmonary artery pressure (via echocardiography)
- Systemic blood pressure
- Adverse effects (GI upset, flushing)
過量
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 藥物參考供持牌獸醫專業人員作臨床決策輔助之用,不能取代專業判斷或廠方最新藥品說明書。