アセプロマジン
**アセプロマジン**は、獣医学において古くから広く利用されているフェノチアジン系神経遮断薬であり、主にその確実な鎮静および精神安定作用のために使用されます。 **臨床上の重要なポイント:** * **鎮痛作用なし:** アセプロマジンには**鎮痛効果が全くありません**。痛みを伴う処置には、適切な鎮痛薬(オピオイドなど)との併用(神経遮断鎮痛)が必須です。 * **心血管系への影響:** α1受容体遮断作用による強力な血管拡張薬であり、頻繁に**低血圧**を引き起こします。循環血液量減少、ショック、または血行動態が不安定な患者には使用を避けるべきです。 * **犬種の感受性:** 超大型犬やサイトハウンド(グレイハウンドなど)は非常に敏感です。**MDR1(ABCB1)遺伝子変異**を持つ犬(コリー、オーストラリアン・シェパードなど)は、大幅な用量減量(25〜50%)が必要です。 * **馬に関する注意事項:** 牡馬において持続的な陰茎脱出または持続勃起症を引き起こす可能性があり、陰茎牽引筋の永久的な麻痺につながる恐れがあります。 歴史的には旅行不安や音響恐怖症に使用されてきましたが、現代の獣医行動学者は、根本的な恐怖やパニックを軽減せずに動物を鎮静させるだけであり、音に対する感受性を高める可能性があるため、これらの状態に対する単独療法としての使用を推奨していません。
作用機序: Acepromazine exerts its effects through multiple receptor antagonisms: * **Dopamine (D2) Receptor Antagonism:** Blocks postsynaptic D2 receptors in the CNS (specifically the basal ganglia and limbic system) → depresses the reticular activating system → produces **sedation and tranquilization**. * **Alpha-1 Adrenergic Antagonism:** Blocks peripheral alpha-1 receptors → causes peripheral vasodilation → leads to **hypotension** and secondary hypothermia. * **Additional Blockade:** Possesses varying degrees of **anticholinergic** (muscarinic), **antihistaminic** (H1), and **antispasmodic** effects. * **Antiemetic Effect:** Blocks dopamine receptors in the Chemoreceptor Trigger Zone (CRTZ) of the medulla. > **Clinical Pearl:** Because of its alpha-blocking properties, administering epinephrine to an acepromazine-induced hypotensive patient can cause **"epinephrine reversal"** (unopposed beta-2 vasodilation), worsening the hypotension. Alpha-agonists like phenylephrine are preferred for treating severe acepromazine-induced hypotension.
動物種別の用量
- Sedation · 0.05-0.1 mg/kg IM · IM
- Sedation · 0.05-0.1 mg/kg IM · IM
- Labeled dose · 0.55-2.2 mg/kg PO or 0.55-1.1 mg/kg IV, IM or SC · PO, IV, IM, SC · Considered by many clinicians to be 10 times greater than necessary.
- Restraint/sedation · 0.025-0.2 mg/kg IV; maximum of 3 mg or 0.1-0.25 mg/kg IM · IV, IM
- Preanesthetic · 0.1-0.2 mg/kg IV or IM; maximum of 3 mg; 0.05-1 mg/kg IV, IM or SC · IV, IM, SC
- To reduce anxiety in the painful patient (not a substitute for analgesia) · 0.05 mg/kg IM, IV or SC; do not exceed 1 mg total dose · IM, IV, SC
- Premedication · 0.03-0.05 mg/kg IM or 1-3 mg/kg PO · IM, PO · Give at least one hour prior to surgery (PO not as reliable).
- As a premedicant with morphine · acepromazine 0.05 mg/kg IM; morphine 0.5 mg/kg IM · IM
- Sedation and premedication (Non-Boxers) · 0.01-0.02 mg/kg · IV · single dose · up to 6 hours · Administer slowly. Generally given as part of a combination with opioids.
- Sedation and premedication (Non-Boxers) · 0.01-0.05 mg/kg · IM/SC · single dose · up to 6 hours · Onset of sedation is 20-30 minutes after IM administration.
投与経路
禁忌
- Significant cardiac disease
- Hypovolemia, hypotension, or shock
- Tetanus or strychnine intoxication
- Intra-arterial injection in horses (can cause severe CNS excitement, seizures, death)
- Use with extreme caution in very young, geriatric, or debilitated animals
- Avoid in racing animals within 4 days of a race
有害事象
- Hypotension and cardiovascular collapse
- Bradycardia (vagally mediated) or reflex tachycardia
- Hypothermia or hyperthermia
- Penile protrusion/prolapse in large animals (especially stallions)
- Prolapse of the membrana nictitans (third eyelid)
- Decreased tear production (especially in cats)
- Paradoxical excitement, restlessness, or aggression
- Transient pain at IM injection sites
- Decreased hematocrit (due to splenic sequestration of RBCs)
薬物相互作用
- Acetaminophen · Possible increased risk for hypothermia
- Antacids · May cause reduced GI absorption of oral phenothiazines
- Antidiarrheal mixtures (Kaolin/pectin, bismuth) · May cause reduced GI absorption of oral phenothiazines
- CNS Depressant Agents (barbiturates, narcotics, anesthetics) · May cause additive CNS depression if used with acepromazine
- Dopamine · Acepromazine may impair the vasopressive action of dopamine
- Emetics · Acepromazine may reduce the effectiveness of emetics
- Epinephrine, Ephedrine · Concomitant use can lead to unopposed beta-activity causing vasodilation and increased cardiac rate (epinephrine reversal)
- Metoclopramide · May increase risks for extrapyramidal adverse effects
- Opiates · May enhance hypotensive effects; dosages of acepromazine are generally reduced when used with an opiate
- Organophosphate Agents · Effects may be potentiated; do not give within one month of worming with these agents
- Phenytoin · Metabolism may be decreased if given concurrently
- Procaine · Activity may be enhanced by phenothiazines
モニタリング
- Cardiac rate, rhythm, and blood pressure (especially in compromised patients)
- Degree of tranquilization and sedation
- Male horses: Monitor to ensure the penis retracts and is not injured
- Body temperature (especially if ambient temperature is very hot or cold)
過量投与
The LD50 in mice is 61 mg/kg IV and 257 mg/kg PO. Dogs have survived oral dosages up to 220 mg/kg, but overdoses can cause serious **hypotension, CNS depression, pulmonary edema, and hyperemia**. **Clinical Signs of Toxicity:** * **Dogs:** Ataxia, sedation, lethargy, depression, protrusion of the third eyelid, somnolence, bradycardia, and recumbency. * **Cats:** Sedation, ataxia, lethargy, protrusion of the third eyelid, and depression. **Treatment:** * Because of relatively low toxicity, most overdoses are handled by monitoring and symptomatic treatment. * Massive oral overdoses should be treated by emptying the gut if possible. * **Hypotension:** Should *not* be treated initially with fluids. If fluids fail to maintain BP, use alpha-adrenergic pressor agents (e.g., phenylephrine). *Note: Avoid epinephrine due to the risk of "epinephrine reversal" causing further vasodilation.* * **Seizures:** May be controlled with barbiturates or diazepam. * **CNS Depression:** Doxapram has been suggested as an antagonist to the CNS depressant effects.
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