クロルプロマジン
クロルプロマジンはプロトタイプのフェノチアジン系誘導体であり、歴史的に獣医学において神経遮断薬および鎮静薬として使用されてきましたが、現在ではより強力で作用時間の短いアセプロマジンに大部分が取って代わられています。 現在では主に小動物の**制吐作用**、特に猫の乗り物酔いの管理に利用されています。 **臨床上の重要なポイント:** * 犬（猫ではない）におけるアポモルヒネ誘発性嘔吐、およびモルヒネ誘発性嘔吐を効果的に抑制します。 * 硫酸銅やジギタリス配糖体による嘔吐は抑制しません。 * **鎮痛作用はほとんどありません**。痛みを伴う状態には適切な鎮痛薬を投与する必要があります。 * 逆説的な興奮や運動失調を引き起こすため、馬への使用は一般的に禁忌です。 * 著しい血管拡張と低血圧を引き起こす可能性があります。投与前に患者に十分な水分補給を行う必要があります。
作用機序: Chlorpromazine acts primarily as a **dopamine (D2) receptor antagonist** in the central nervous system. * **Antiemetic effect:** Blocks D2 receptors in the Chemoreceptor Trigger Zone (CRTZ) of the medulla → inhibits emetic signaling to the vomiting center. * **Sedative effect:** Antagonizes central **histamine (H1)**, **alpha-1 adrenergic**, and **dopamine** receptors → depresses the reticular activating system. * **Cardiovascular effect:** Peripheral **alpha-1 adrenergic blockade** → vasodilation and potential hypotension. * Also possesses weak anticholinergic (muscarinic M1 blockade) and antiserotonergic properties.
動物種別の用量
- General use · 0.55-4.4 mg/kg IV, 2.2-6.6 mg/kg IM · IV/IM · Once
- General use · 0.55-4.4 mg/kg IV, 2.2-6.6 mg/kg IM · IV/IM · Once
- General use · 2-3.5 mg/kg IV q5-6h · IV · q5-6h
- As an antiemetic · 0.5 mg/kg IV, IM or SC three to four times daily · IV/IM/SC · q6-8h
- As an antiemetic · 2 mg (total dose) per cat PO q12h · PO · q12h
- As a preanesthetic · up to 1.1 mg/kg IM 1-1.5 hours prior to surgery · IM · Once
- Premedication for cattle undergoing standing procedures · Up to 1 mg/kg IM · IM · Once · May cause regurgitation if animal undergoes general anesthesia
- Premedication · 1 mg/kg IM · IM · Once
- Premedication · 0.55-3.3 mg/kg IV; 2-4 mg/kg IM · IV/IM · Once
投与経路
禁忌
- Horses (generally not recommended due to severe ataxia and panic reactions)
- Rabbits (IM injection causes severe muscle discomfort and swelling)
- Hypovolemia or shock
- Tetanus or strychnine intoxication (due to extrapyramidal effects)
有害事象
- Hypotension
- CNS stimulation (paradoxical)
- Bradycardia or tachycardia
- Extrapyramidal signs in cats (tremors, shivering, rigidity, loss of righting reflexes)
- Lethargy
- Diarrhea
- Loss of anal sphincter tone
- Ataxia, excitation, and panic reactions in horses
- Hypothermia or hyperthermia
薬物相互作用
- Acetaminophen · Possible increased risk for hypothermia
- Antacids · May cause reduced GI absorption of oral phenothiazines
- Antidiarrheal mixtures (e.g., kaolin/pectin, bismuth subsalicylate) · May cause reduced GI absorption of oral phenothiazines
- CNS Depressant Agents (barbiturates, narcotics, anesthetics) · May cause additive CNS depression
- Dipyrone · May cause serious hypothermia
- Epinephrine · Phenothiazines block alpha-adrenergic receptors; concomitant epinephrine can lead to unopposed beta-activity causing vasodilation and increased cardiac rate (epinephrine reversal)
- Opiates · May enhance hypotensive effects; chlorpromazine dosages may need reduction
- Organophosphate Agents · Effects may be potentiated; do not give phenothiazines within one month of worming with these agents
- Paraquat · Toxicity may be increased by chlorpromazine
- Phenytoin · Metabolism may be decreased if given concurrently
- Physostigmine · Toxicity may be enhanced by chlorpromazine
- Procaine · Activity may be enhanced by phenothiazines
- Propranolol · Increased blood levels of both drugs may result
モニタリング
- Cardiac rate, rhythm, and blood pressure (if indicated and possible)
- Degree of tranquilization and anti-emetic activity
- Body temperature (especially in extreme ambient temperatures)
過量投与
Small overdoses typically cause somnolence. Larger overdoses can cause serious effects including **coma, agitation/seizures, ECG changes/arrhythmias, hypotension, and extrapyramidal effects**. * **Treatment:** Most overdoses are managed with supportive care and monitoring. Massive oral overdoses should be treated by emptying the gut if possible. * **Hypotension Management:** Do NOT treat hypotension with epinephrine (due to epinephrine reversal). Use **phenylephrine** or **norepinephrine** (levarterenol). * **Seizure Management:** Control seizures with barbiturates or diazepam.
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。