フェニルプロパノールアミン
フェニルプロパノールアミン（PPA）は非選択的交感神経刺激アミンであり、獣医療では主に避妊手術後の雌犬に見られる**尿道括約筋機能不全（USMI）**に関連する**尿失禁**の管理に使用されます。 歴史的には鼻閉改善薬として使用されてきましたが、獣医療における主な適応は、膀胱頸部および近位尿道の平滑筋緊張を高める作用に基づいています。 **臨床上のポイント：** * PPAは犬の後天性尿失禁に対して非常に有効であり、成功率はしばしば75〜85％を超えます。 * 交感神経刺激薬であるため、全身性の作動性作用、特に高血圧や行動の変化（落ち着きのなさ、不安）を引き起こす可能性があります。 * 米国では、メタンフェタミン合成の前駆物質として使用される可能性があるため、リスト1化学物質に分類されており、購入に特定の制限が課される場合があります。
作用機序: 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.
動物種別の用量
- 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
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
- Glaucoma
- Prostatic hypertrophy
- Hyperthyroidism
- Diabetes mellitus
- Cardiovascular disorders
- Hypertension
- Severe renal or hepatic disease
有害事象
- Restlessness
- Anxiety
- Irritability
- Urine retention
- Tachycardia
- Hypertension
- Anorexia
- Rare reports of 'stroke' in dogs
- Panting
薬物相互作用
- 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
モニタリング
- 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)
過量投与
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 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。