苯丙醇胺
苯丙醇胺 (PPA) 是一種非選擇性擬交感神經胺，在獸醫學中主要用於治療與**尿道括約肌機能不全 (USMI)** 相關的**尿失禁**，特別是在已結紮的雌性犬隻中。 雖然它過去曾被用作鼻腔去充血劑，但其主要的獸醫適應症依賴於它能增加膀胱頸和近端尿道平滑肌張力的能力。 **臨床要點：** * PPA 對於犬隻後天性尿失禁非常有效，成功率通常超過 75-85%。 * 由於它是一種擬交感神經藥物，可能會引起全身性腎上腺素能副作用，最明顯的是高血壓和行為改變（焦躁不安、焦慮）。 * 在美國，由於其可能被用作合成甲基安非他命的前驅物，因此被列為第一類化學品，購買時可能會受到特定限制。
作用機制: Phenylpropanolamine acts primarily as an **indirect-acting sympathomimetic**, though it may have some direct receptor agonist activity. * **Mechanism:** It stimulates the release of endogenous **norepinephrine** from presynaptic nerve terminals. * **Pathway:** Released norepinephrine binds to **alpha-1 adrenergic receptors** located in the smooth muscle of the internal urethral sphincter and bladder neck → **increased sphincter tone** → prevention of urine leakage. * It also stimulates beta-adrenergic receptors, which can contribute to systemic cardiovascular effects (e.g., increased heart rate and contractility). * **Note:** Prolonged use or excessive dosing frequency can theoretically deplete norepinephrine from storage sites, leading to tachyphylaxis (decreased response), though this is rarely documented in dogs or cats treated for incontinence.
各物種劑量
- Urethral sphincter hypotonus · 12.5 mg PO q8h · PO · q8h
- Urethral sphincter hypotonus · 1-1.5 mg/kg PO q8h · PO · q8h
- Urethral sphincter hypotonus · 1.1 -2.2 mg/kg PO two to three times daily · PO · q8-12h
- Urethral sphincter hypotonus · 12.5-50 mg (total dose) or 1-2 mg/kg PO q8h · PO · q8h
- Urethral sphincter hypotonus · Dogs weighing less than 40 lbs: ½ capsule PO daily. Dogs 40-100 lbs: 1 capsule PO daily. Dogs weighing >100 lbs: 1.5 capsules PO per day. · PO · q24h · Using the time-release 75 mg capsules
- Urethral sphincter hypotonus · 1-1.5 mg/kg PO two to three times a day · PO · q8-12h · Controls 74-92% of dogs with primary sphincter mechanism incontinence. Over half of dogs not responding to regular PPA will respond to sustained-release PPA.
- Urethral sphincter hypotonus · 5-50 mg per dog PO q8h or 1.5 mg/kg PO q8h-12h · PO · q8-12h
- Retrograde ejaculation · 3-4 mg/kg PO twice daily · PO · q12h · May be tried
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
- Glaucoma
- Prostatic hypertrophy
- Hyperthyroidism
- Diabetes mellitus
- Cardiovascular disorders
- Hypertension
- Severe renal or hepatic disease
不良反應
- Restlessness
- Anxiety
- Irritability
- Urine retention
- Tachycardia
- Hypertension
- Anorexia
- Rare reports of 'stroke' in dogs
- Panting
藥物相互作用
- Halothane · Increased risk of arrhythmias. Propranolol may be administered should these occur. · major
- Monoamine Oxidase (MAO) Inhibitors (e.g., amitraz, selegiline) · Should not be given within two weeks of receiving MAOIs due to risk of severe hypertension and toxicity.
- NSAIDs (including aspirin) · Increased chance of hypertension if given concomitantly.
- Reserpine · Increased chance of hypertension if given concomitantly.
- Other Sympathomimetic Agents (e.g., ephedrine) · Should not be administered together as increased toxicity may result.
- Tricyclic Antidepressants (e.g., clomipramine, amitriptyline) · Increased chance of hypertension if given concomitantly.
- NSAIDs · Increased risk of hypertension · moderate
- Monoamine Oxidase Inhibitors (MAOIs) · Risk of severe hypertensive crisis · major
- Tricyclic Antidepressants · Increased sympathomimetic effects and risk of hypertension · major
監測
- Clinical effectiveness (reduction in urine leakage)
- Adverse effects (restlessness, irritability, anorexia)
- Blood pressure
- Clinical response (reduction in urinary incontinence)
- Heart rate and rhythm
- Behavioral changes (restlessness, pacing)
過量
Clinical signs of overdosage may consist of an exacerbation of adverse effects (restlessness, anxiety). **Severe Overdose Signs:** * **Cardiovascular:** Hypertension to rebound hypotension, bradycardias to tachycardias, and cardiovascular collapse. * **CNS:** Stimulation progressing to coma. * *Case report:* A dog ingesting 48 mg/kg developed ventricular tachycardia and myocardial necrosis (resolved within 6 months). **Treatment:** * If recent, empty the stomach using usual precautions and administer charcoal and a cathartic. * Treat clinical signs supportively. * > **WARNING:** Do NOT use propranolol to treat hypertension in bradycardic patients. Do NOT use atropine to treat bradycardia. * Hypertension may be managed with a phenothiazine (e.g., acepromazine at very low doses such as 0.02 mg/kg IV or IM). If unsuccessful, consider a CRI of nitroprusside. * Contact an animal poison control center for further 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。