Tadalafil
Tadalafil is a long-acting **phosphodiesterase type 5 (PDE5) inhibitor** primarily used in veterinary medicine for the management of **pulmonary arterial hypertension (PAH)** in dogs. * **Clinical Pearl**: Compared to sildenafil (Viagra®), tadalafil has a significantly longer half-life, allowing for once-daily or every-other-day dosing, which greatly improves owner compliance. * It is often used as an adjunctive therapy alongside conventional heart failure medications (e.g., pimobendan, diuretics, ACE inhibitors) when right-sided heart pressures remain elevated. * *Note*: Clinical data and published literature in veterinary species are currently very limited, and the medication can be cost-prohibitive.
กลไกการออกฤทธิ์: 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).
ขนาดยาตามชนิดสัตว์
- 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
ขนาดยาเป็นข้อมูลอ้างอิงทางคลินิกสำหรับสัตวแพทย์ผู้มีใบอนุญาต โปรดตรวจสอบกับฉลากล่าสุดและผู้ป่วยแต่ละรายเสมอ
วิธีการให้ยา
ข้อห้ามใช้
- Concurrent use of any form of organic nitrates (regularly or intermittently)
- Serious hypersensitivity to tadalafil
อาการไม่พึงประสงค์
- 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)
อันตรกิริยาระหว่างยา
- 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
การติดตาม
- Clinical efficacy (improved syncope, cough, respiratory effort)
- Pulmonary artery pressure (via echocardiography)
- Systemic blood pressure
- Adverse effects (GI upset, flushing)
การได้รับยาเกินขนาด
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.
ข้อมูลอ้างอิงยาของ VetSheet มีไว้สำหรับสัตวแพทย์ผู้มีใบอนุญาตเพื่อช่วยในการตัดสินใจทางคลินิก ไม่ใช่สิ่งทดแทนการวินิจฉัยของผู้เชี่ยวชาญหรือฉลากล่าสุดของผู้ผลิต