美沙酮
Methadone
Methadone hydrochloride
別名: Dolophine · Methadose · Diskets · Comfortan · Synthadon · Amidine HCl · amidone HCl · methadoni hydrochloridum · Phenadone · Methadone hydrochloride · Metadona
由 VetSheet 獸醫團隊審訂更新於 2026年4月5日本內容以實證獸醫文獻為本
經審核的 v13 劑量證據
經審核的非計算證據經審核的非計算證據 (1)
僅供證據參考，不會自動計算
Anesthesia premedication (extra-label)
Anesthesia premedication (extra-label): Methadone 0.1 – 0.6 mg/kg IV, IM, or SC 70,74
必須一併考量的臨床脈絡 (2)
- NOTE: All listed dosages are based on the methadone HCl salt formulation (10 mg methadone HCl is equivalent to ≈8.9 mg of methadone). Most products are labeled with methadone HCl strength but check before administering to patients.
- Methadone injection should be stored at room temperature of 20°C to 25°C (68°F-77°F) and protected from light. Store vials in the manufacturer’s carton until ready for use.
劑量為合格獸醫專業人員的臨床參考。請務必對照最新仿單及個別病患確認。
概覽
美沙酮是一種合成的強效 μ-鴉片類受體促效劑 (mu-opioid agonist)，在獸醫學中常作為犬貓的麻醉前給藥與鎮痛藥。與嗎啡相比，它在靜脈注射時較不易引起組織胺釋放，且較少導致嘔吐或過度鎮靜。
臨床重點與藥理優勢：
- 三重機制： 與大多數傳統鴉片類藥物不同，美沙酮不僅是 μ-受體促效劑，同時也是 非競爭性 NMDA 受體拮抗劑 以及 單胺類（血清素與正腎上腺素）再回收抑制劑。
- 神經病理性疼痛： 由於其 NMDA 拮抗作用，美沙酮在治療頑固性疼痛、神經病理性疼痛以及預防中樞敏感化（「痛覺過敏」或「wind-up」現象）方面特別有價值。
- 生體可用率： 在犬隻的口服生體可用率極差，因此在獸醫臨床上標準給藥途徑為注射（IV、IM、SC）。
- 法規： 由於對人類具有高度成癮與濫用風險，本藥屬於第二級管制藥品 (Schedule II)。
作用機轉
Methadone provides analgesia through a unique, multi-modal mechanism of action:
- Mu-Opioid Receptor (MOR) Agonism: Binds to MORs in the central nervous system → inhibits adenylyl cyclase → decreases cAMP → promotes opening of inward-rectifying potassium channels and closing of voltage-gated calcium channels → hyperpolarization of neurons and decreased release of nociceptive neurotransmitters (e.g., Substance P, glutamate).
- NMDA Receptor Antagonism: Acts as a non-competitive antagonist at the N-methyl-D-aspartate (NMDA) receptor → blocks glutamate binding → reduces central sensitization and hyperalgesia.
- Monoamine Reuptake Inhibition: Inhibits the presynaptic reuptake of serotonin (5-HT) and norepinephrine (NE) → increases monoamine concentrations in the synaptic cleft → enhances descending inhibitory pain pathways in the spinal cord.
安全性與警告
禁忌症
- Late-term pregnancy (due to risks of respiratory depression and stillbirths)
- Known hypersensitivity to methadone
- No specific contraindications available in the monograph, but use with caution in patients with severe respiratory compromise or hepatic impairment.
不良反應
- Panting
- Whining or vocalization
- Defecation
- Constipation
- Bradycardia
- Pronounced CNS excitement (in horses at IV doses ≥ 0.1 mg/kg)
- Respiratory depression (primarily under general anaesthesia)
- Transient excitation (when given IV)
- Salivation (when given via oral transmucosal route in cats due to preservatives)
- Constriction of gastrointestinal sphincters (e.g., pyloric sphincter)
- Reduction in gastrointestinal motility (with prolonged use)
- Neonatal sedation (crosses the placenta)
注意事項
All opiates should be used with caution in patients with heart failure, hypertension, head injuries, elevated CSF pressures, and in geriatric or severely debilitated patients.
Note: Methadone can increase plasma amylase and lipase values up to 24 hours following administration due to increased biliary tract pressure.
藥物交互作用
May increase risks for arrhythmias
Potentiates sedative and analgesic effects; combination with medetomidine may cause severe hypoxemia in dogs breathing room air
May increase methadone levels in humans (does not appear to be true for dogs)
May increase risks for arrhythmias
May cause increased CNS or respiratory depression
May increase potential for electrolyte abnormalities
Opiates may decrease diuretic efficacy in CHF patients
May inhibit metabolism of methadone and increase levels in humans (does not appear to be true for dogs)
Potential for severe CNS/behavioral reactions; concomitant use should be avoided
Methadone may enhance neuromuscular blockade
May decrease methadone levels in humans (probably does not affect dogs)
May decrease methadone levels in humans (probably does not affect dogs)
May increase methadone levels
May decrease methadone levels in humans (probably does not affect dogs)
Methadone may exacerbate the effects of tricyclic antidepressants
Opiates may potentiate anticoagulant activity
Methadone may increase zidovudine levels
Increased CNS or respiratory depression
監測
- Analgesic or preanesthetic efficacy
- Respiratory rate and depth (monitor for respiratory depression, especially at higher doses)
- Heart rate (bradycardia)
- CNS depression or excitation
- Respiratory rate and depth (especially under general anaesthesia)
- Pain scores (due to individual variation in response)
- Level of sedation
- Gastrointestinal motility (with prolonged use)
藥物動力學
半衰期
吸收
In dogs, methadone has poor oral bioavailability (not significantly affected by ketoconazole or omeprazole). Subcutaneous bioavailability is ~80% with peak levels around 1 hour. In horses, orally administered methadone is well absorbed but rapidly eliminated.
分佈
Highly lipid-soluble and widely distributed. In humans, it is extensively bound to plasma proteins (60-90%).
代謝
Hepatic. Unlike in humans, CYP3A does not appear to be a major metabolic pathway for methadone biotransformation in dogs. Metabolites are inactive.
排除
In dogs, clearance is about 25-30 mL/kg/min.
過量
Overdosage may produce profound respiratory and/or CNS depression in most species. Newborns are particularly susceptible. Other toxic effects include cardiovascular collapse, hypothermia, and skeletal muscle hypotonia.
Treatment:
- Naloxone is the reversal agent of choice for treating respiratory depression. In massive overdoses, naloxone doses may need to be repeated because naloxone's effects might diminish before sub-toxic levels of methadone are attained.
- Mechanical respiratory support should be considered in severe cases.
- Dialysis, charcoal hemoperfusion, or forced diuresis do not appear to be beneficial.
可用產品
劑型
- Injection
- Oral tablets
- Dispersible tablets
- Oral solution/liquid concentrate
- Injectable: 10 mg/ml solution (including generic preservative-free preparations)
- Oral: 10 mg tablets
獸醫用
- Comfortan 10 mg/ml solution for injection
- Synthadon 10 mg/ml solution for injection
人用標示
- Methadone HCl Injection: 10 mg/mL
- Methadone HCl Oral Tablets: 5 mg & 10 mg
- Methadone HCl Dispersible Tablets: 40 mg
- Methadone HCl Oral Solution/Liquid Concentrate: 1 mg/mL, 2 mg/mL & 10 mg/mL
- Generic methadone 10 mg tablets
各地核准狀態
Authorized veterinary preparations available.
Subject to strict safe custody and register requirements.
暫無法規資料: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
儲存與穩定性
Store at room temperature and protect from light. Methadone injection is reportedly stable when mixed in a syringe with acepromazine, but is NOT compatible with pentobarbital, phenobarbital, amobarbital, or thiopental.
飼主須知
美沙酮是一種強效且受嚴格管制的鴉片類鎮痛藥物。當以注射方式給予時，通常是在動物醫院內由獸醫專業人員直接監督下進行。
如果您的獸醫師開立口服美沙酮讓寵物在家控制疼痛：
- 請嚴格遵守指示劑量。 未經獸醫師同意，切勿自行增加或減少劑量。
-
極度危險： 請將此藥物存放在安全且兒童與其他寵物絕對接觸不到的地方。人類（尤其是兒童）誤食可能導致致命的呼吸抑制。
- 請觀察寵物是否出現輕微嗜睡、喘氣、發出嗚嗚聲或便秘等副作用。
- 若出現以下情況請立即就醫： 寵物變得極度昏睡、呼吸困難，或呼吸變得異常緩慢。
VetSheet 藥物參考供合格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商最新仿單。