フェノキシベンザミン
Phenoxybenzamine
Phenoxybenzamine HCl
別名: Dibenzyline · Dibenyline · SKF-688A · Dibenzyran · Fenoxene · Phenoxybenzaminum
VetSheet 獣医チームが監修更新日 2026年4月5日エビデンスに基づく獣医学リファレンス
用量は獣医専門家向けの臨床参考資料です。必ず最新の医薬品情報および個別症例に基づいて確認してください。
動物種別用量
🌎 NA — North America🌍 EU — Europe
犬
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Functional urethral obstruction | 0.25 mg/kg | PO | q12-24h | — | 🌎 NA |
| Functional urethral obstruction | 0.25 mg/kg | PO | q12h | — | 🌎 NA |
| Functional urethral obstruction | 0.25-0.5 mg/kg | PO | once or twice daily | — | 🌎 NA |
| Functional urethral obstruction | 5-15 mg (total dose) | PO | q12h | — | 🌎 NA |
| Hypertension associated with pheochromocytoma (pre-surgical) | Initially 0.5 mg/kg, gradually increase every few days until clinical signs of hypotension, adverse reactions, or max dosage of 2.5 mg/kg is attained | PO | twice daily | 1-2 weeks prior to surgery | 🌎 NA |
| Hypertension associated with pheochromocytoma (medical management) | Initial dose 0.25 mg/kg, gradually increase every few days until signs of hypotension, adverse reaction, or max dosage of 2.5 mg/kg is attained | PO | twice daily | Long-term | 🌎 NA |
| Adjunctive treatment of endotoxicosis | 0.25-0.5 mg/kg | PO | q6h | — | 🌎 NA |
- Functional urethral obstruction: Alternative dose: 2.5-20 mg (total dose) PO q12-24h
- Hypertension associated with pheochromocytoma (pre-surgical): Continue until the time of surgery. Close perioperative monitoring is critical.
- Hypertension associated with pheochromocytoma (medical management): Beta-blockers may be added for severe tachycardia, but NEVER without prior alpha-blockade to avoid severe hypertension.
- Adjunctive treatment of endotoxicosis: Use with appropriate antimicrobials, steroids, and supportive care.
猫
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Functional urethral obstruction | 2.5-7.5 mg/cat | PO | once to twice daily | — | 🌎 NA |
| Functional urethral obstruction | 1.25-7.5 mg (total dose) | PO | q12-24h | — | 🌎 NA |
| Functional urethral obstruction | 2.5-10 mg (total dose) | PO | q24h | — | 🌎 NA |
| Short-term treatment of hypertension | 0.5 mg/kg | PO | q12h | — | 🌎 NA |
| Short-term treatment of hypertension | 2.5 mg (total dose) increasing by 2.5 mg up to a maximum of 10 mg (total dose) | PO | q12h | — | 🌎 NA |
| Short-term treatment of hypertension | 2.5-7.5 mg per cat | PO | q8-12h | — | 🌎 NA |
馬
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Decrease urethral sphincter tone in bladder paresis | 0.7 mg/kg | PO | 4 times a day | — | 🌎 NA |
| Adjunctive treatment of laminitis (developmental phase) | 1 mg/kg | IV | q12h | for 2 doses | 🌎 NA |
| Treatment of profuse, watery diarrhea | 200-600 mg | — | q12h | — | 🌎 NA |
- Decrease urethral sphincter tone in bladder paresis: Used in combination with bethanechol at 0.25-0.75 mg/kg PO 2-4 times a day.
用量は獣医専門家向けの臨床参考資料です。必ず最新の医薬品情報および個別症例に基づいて確認してください。
概要
フェノキシベンザミンは、長時間作用型の非競合的α-アドレナリン受容体拮抗薬です。
獣医療では主に以下の目的で使用されます：
- 小動物：機能的尿道閉塞や排尿筋無反射を治療するための内尿道括約筋の緊張低下。また、褐色細胞腫の患者において、腫瘍の外科的操作中の致命的な高血圧クリーゼを予防するための重要な術前投与薬でもあります。
- 馬：初期の蹄葉炎、分泌性下痢、膀胱不全麻痺の管理などの特殊な用途。
臨床のポイント：フェノキシベンザミンは受容体に不可逆的に結合するため、その効果は長く続き、新しい受容体が合成されることによってのみ回復します。このプロセスには数日かかります。
作用機序
Phenoxybenzamine covalently and irreversibly binds to alpha-1 and alpha-2 adrenergic receptors → non-competitive blockade of circulating epinephrine and norepinephrine → profound vasodilation and relaxation of smooth muscle.
- Urinary Tract: Blockade of alpha receptors in the trigone and internal urethral sphincter → decreased urethral resistance → facilitation of bladder emptying.
- Cardiovascular: Blockade of vascular alpha receptors → decreased peripheral vascular resistance → lowered blood pressure (often causing reflex tachycardia).
Because the binding is irreversible, the effect is often described as a 'chemical sympathectomy'. It has no effect on beta-adrenergic or parasympathetic receptors.
安全性・警告
禁忌
- Conditions where hypotension is undesirable (e.g., shock, unless fluid replacement is adequate)
- Horses with clinical signs of colic
- Glaucoma (relative contraindication)
- Diabetes mellitus (relative contraindication)
有害事象
- Hypotension (postural/orthostatic)
- Hypertension (rebound)
- Miosis
- Increased intraocular pressure
- Tachycardia (reflex)
- Sodium retention
- Inhibition of ejaculation
- Nasal congestion
- Weakness or dizziness
- Gastrointestinal effects (nausea, vomiting)
- Constipation (specifically noted in horses)
注意事項
Use with extreme caution in patients with congestive heart failure (CHF) or other heart disease, as drug-induced tachycardia can occur. Use cautiously in patients with renal damage or cerebral/coronary arteriosclerosis.
Pregnancy: FDA Category C. Animal studies (guinea pigs) have shown abnormalities in the closure of the patent ductus. Use only if benefits outweigh risks.
医薬品相互作用
Epinephrine reversal: If used with drugs that have both alpha- and beta-adrenergic effects, increased hypotension, vasodilation, or tachycardia may result due to unopposed beta effects.
Phenoxybenzamine will antagonize the effects of alpha-adrenergic sympathomimetic agents.
Phenoxybenzamine can antagonize the hypothermic effects of reserpine.
Increased risk of first dose hypotensive effect; if used for phaeochromocytoma, beta-blockers must only be started after alpha blockade is in place to avoid hypertensive crisis.
Increased risk of first dose hypotensive effect.
Phenoxybenzamine will antagonize the effects of these agents.
監視
- Clinical efficacy (e.g., adequate urination, ease of voiding)
- Blood pressure (monitor for hypotension)
- Heart rate (monitor for reflex tachycardia)
- Heart rate and rhythm
- Urine output and ease of urination
薬物動態
吸収
Variably absorbed from the GI tract, with a bioavailability of 20-30% in humans. Onset of action is slow (several hours) and increases over several days after regular dosing. Effects persist for 3-4 days after discontinuation.
分布
Highly lipid soluble and may accumulate in body fat. Unknown if it crosses the placenta or enters milk.
代謝
Metabolized (dealkylated) in the liver.
消失
Excreted in both the urine and bile.
過剰投与
Overdosage may yield signs of postural hypotension (dizziness, syncope), tachycardia, vomiting, lethargy, or shock.
Treatment:
- Empty the gut if ingestion was recent and there are no contraindications.
- Treat hypotension with aggressive intravenous fluid support.
- DO NOT USE EPINEPHRINE (causes paradoxical further drop in blood pressure due to unopposed beta-adrenergic vasodilation).
- Most standard vasopressors are ineffective due to the alpha-blockade. Intravenous norepinephrine (levarterenol) may be beneficial if clinical signs are severe.
製品
製剤
- Capsules
- 10 mg oral capsule
- 50 mg/ml injectable solution
ヒト用医薬品
- Phenoxybenzamine HCl Capsules: 10 mg (Dibenzyline)
- Dibenyline 10 mg capsules
- Phenoxybenzamine 50 mg/ml solution
規制ステータス
POM (Prescription Only Medicine)
POM (Prescription Only Medicine)
規制データなし: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
保管・安定性
Capsules should be stored at room temperature in well-closed containers.
飼主向け情報
フェノキシベンザミンは、尿道の筋肉をリラックスさせてペットの排尿を助けたり、特定の副腎腫瘍に関連する高血圧を管理するために処方されます。
- 忍耐が必要です：ペットの排尿に対する完全な効果が現れるまでに1週間以上かかる場合があります。獣医師の指示がない限り、早期に投薬を中止しないでください。
- 食事と一緒に与える：この薬を食事と一緒に与えることで、胃の不調（吐き気や嘔吐）を軽減できる場合があります。
- 低血圧に注意：この薬は血管を拡張させるため、血圧が低下する可能性があります。ペットが虚弱に見えたり、めまいを起こしたり、立ち上がった後に倒れたりした場合は、すぐに獣医師に連絡してください。
- 飲み忘れ：飲み忘れた場合は、気づいた時点ですぐに与えてください。ただし、絶対に1度に2回分を与えないでください。
VetSheet医薬品リファレンスは獣医専門家の臨床意思決定支援を目的としており、専門的判断または製造業者の最新医薬品情報の代替にはなりません。