哌唑嗪
哌唑嗪（Prazosin）是一種高度選擇性的 **Alpha-1 腎上腺素受體阻斷劑**（交感神經抑制劑）。 在獸醫學中，雖然它曾被用作平衡型血管擴張劑（同時降低前負荷與後負荷）以輔助治療充血性心衰竭（CHF）及全身性或肺動脈高壓，但目前最主要的臨床應用是**下泌尿道疾病的管理**。 **臨床要點：** * **尿道放鬆：** 哌唑嗪能極為有效地放鬆內尿道括約肌的平滑肌。它是治療功能性尿道阻塞的常規藥物，特別適用於「尿道阻塞的貓咪」（貓自發性膀胱炎/FLUTD）以及患有反射性協調不良或前列腺疾病的犬隻。 * **心血管特性：** 與肼屈嗪（Hydralazine）不同，哌唑嗪能同時擴張動脈與靜脈端，且通常不會引發反射性心搏過速或增加腎素（Renin）的釋放。
作用機制: **Prazosin** competitively binds to and blocks **post-synaptic alpha-1 adrenergic receptors**. * **Genitourinary Tract:** Blockade of alpha-1 receptors in the trigone of the bladder and the proximal urethra → **smooth muscle relaxation** → decreased urethral resistance → facilitates micturition and relieves functional obstruction. * **Cardiovascular System:** Blockade of alpha-1 receptors on vascular smooth muscle → **vasodilation** of both arterioles and veins → decreased peripheral vascular resistance (afterload) and decreased venous return (preload) → lowered systemic blood pressure and reduced right atrial pressure.
各物種劑量
- Decrease urethral resistance · 0.5 mg (total dose) PO q8h or 0.03 mg/kg IV · PO/IV · q8h (PO)
- Decrease urethral resistance · 0.03 mg/kg IV · IV
- Functional urethral obstruction · 0.25-0.5 mg/cat (total dose) PO q12-24h · PO · q12-24h
- Urethral spasm · 0.25-1 mg/cat (total dose) PO q8-12h · PO · q8-12h · Initially give for 5-7 days then wean off if possible
- Reduce urethral tone · 0.5 mg/cat (total dose) PO once to two times a day · PO · q12-24h
- Adjunctive treatment of heart failure · 1 mg PO three times daily for dogs weighing less than 15 kg; 2 mg three times daily PO for dogs weighing more than 15 kg · PO · q8h
- Hypertension · 1-4 mg (total dose) PO q12-24 hours · PO · q12-24h
- Hypertension in a large dog · 1 mg (total dose) PO q8-12h · PO · q8-12h
- Decrease urethral resistance · 1 mg per 15 kg of body weight PO q8h · PO · q8h
- Functional urethral obstruction · 1 mg/15 kg of body weight PO q8-24h · PO · q8-24h
- Decrease urethral resistance · 1 mg per 15 kg of body weight PO q12-24h · PO · q12-24h
給藥途徑
禁忌症
- Preexisting hypotensive conditions
- Pre-existing hypotension
- Hypovolemia
- Known hypersensitivity to alpha-blockers
不良反應
- Hypotension (including orthostatic hypotension/syncope)
- Lethargy
- Dizziness
- Nausea
- Vomiting
- Diarrhea
- Constipation
- Tachyphylaxis (drug tolerance)
- Hypotension (especially first-dose effect)
- Lethargy / Weakness
- Dizziness / Syncope
- Gastrointestinal upset (vomiting, diarrhea)
- Reflex tachycardia
藥物相互作用
- Beta-blocking agents (e.g., propranolol) · May enhance the postural hypotensive effects seen after the first dose of prazosin
- Clonidine · May decrease prazosin antihypertensive effects
- Sildenafil (and other PDE inhibitors) · May increase risk for hypotension
- Verapamil or Nifedipine · May cause synergistic hypotensive effects when used concomitantly with prazosin
- Amlodipine · Additive hypotensive effects · moderate
- ACE Inhibitors (e.g., Benazepril, Enalapril) · Increased risk of severe hypotension · moderate
- Beta-blockers (e.g., Propranolol) · Exacerbation of postural hypotension · moderate
- Sildenafil · Profound hypotension · major
監測
- Baseline thoracic radiographs
- Mucous membrane color
- Capillary refill time (CRT)
- Arterial blood pressure
- Venous PO2 (if possible)
- Systemic blood pressure
- Heart rate
- Urine output and ease of urination (if used for urethral spasm)
過量
Based on ASPCA APCC data (2008-2009): * **Dogs:** Common findings include hyperactivity, tachycardia, hyperthermia, panting, and agitation. * **Cats:** Common findings include tachycardia. **Treatment:** * Evacuate gastric contents and administer activated charcoal using standard precautionary measures if ingestion was recent and cardiovascular status is stable. * Monitor heart rate and blood pressure. * Treat shock using volume expanders and pressor agents if necessary. * Monitor and support renal function.
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