異丙嗪
異丙嗪是一種吩噻嗪類衍生物，在獸醫學中主要用作止吐藥和抗組織胺藥。 * **主要用途**：偶爾用於控制犬貓的噁心和嘔吐，也曾嘗試用於治療異位性皮膚炎犬隻的搔癢（但對後者的療效通常不佳）。 * **藥理特徵**：雖然在結構上與乙醯丙嗪 (acepromazine) 等鎮靜劑相似，但異丙嗪的特點在於其強效的抗組織胺特性，同時兼具止吐、抗膽鹼、鎮靜和輕微的局部麻醉作用。 > **臨床提示**：與較新的標靶止吐藥（如 maropitant、ondansetron）或標準抗組織胺藥（如 diphenhydramine）相比，異丙嗪在現代獸醫臨床中的處方相對較少，這主要是因為它可能引起鎮靜和錐體外症候群等副作用。
作用機制: Promethazine exerts its effects through competitive antagonism at multiple receptor sites centrally and peripherally: * **H1-Receptor Antagonism**: Competitively blocks histamine at H1 receptors → reduces allergic responses and pruritus. * **D2-Dopaminergic Antagonism**: Blocks dopamine receptors in the Chemoreceptor Trigger Zone (CRTZ) of the medulla → provides central **antiemetic** effects. * **Muscarinic Antagonism**: Blocks acetylcholine at muscarinic receptors → contributes to antiemetic efficacy and causes anticholinergic side effects (e.g., dry mouth). * **Alpha-1 Adrenergic Antagonism**: Blocks peripheral alpha-1 receptors → can lead to vasodilation and subsequent hypotension.
各物種劑量
- As an antiemetic · 2 mg/kg PO or IM once daily · PO/IM · q24h
- As an antihistamine · 0.2-0.4 mg/kg PO three to four times a day · PO · q6-8h
- As an antihistamine · 1-2 mg/kg PO q12h · PO · q12h
- As an antiemetic · 2 mg/kg PO or IM once daily · PO/IM · q24h
- As an antihistamine · 0.2-0.4 mg/kg PO three to four times a day · PO · q6-8h
- As an antihistamine · 1-2 mg/kg PO q12h · PO · q12h
劑量為合格獸醫專業人員的臨床參考。請務必對照最新藥品仿單及個別病患確認。
給藥途徑
禁忌症
- Hypovolemia or shock (due to hypotensive effects)
- Tetanus or strychnine intoxication (due to extrapyramidal effects)
- Human label black box warning: Contraindicated in children < 2 years old (fatal respiratory depression)
- Known hypersensitivity to phenothiazines
- Severe central nervous system depression
- Comatose patients
- Use with caution in patients with seizure disorders
- Use with caution in patients with severe hepatic or cardiovascular disease
不良反應
- Sedation or lethargy
- Anticholinergic effects (dry mouth, urinary retention, decreased GI motility)
- Hypotension (especially with rapid IV administration or in hypovolemic patients)
- Extrapyramidal signs (tremors, rigidity, torticollis) - rare but possible
- Sedation / Lethargy
- Dry mucous membranes (anticholinergic effect)
- Tachycardia
- Hypotension
- Paradoxical excitation (especially in cats)
- Gastrointestinal disturbances
藥物相互作用
- 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.
- Atropine & other anticholinergics · May have additive anticholinergic effects when used with promethazine.
- CNS Depressant Agents (barbiturates, narcotics, anesthetics) · May cause additive CNS depression if used with phenothiazines.
- Epinephrine · Phenothiazines block alpha-adrenergic receptors; concomitant epinephrine can lead to unopposed beta-activity causing vasodilation and increased cardiac rate (epinephrine reversal). · major
- Metoclopramide · Phenothiazines may potentiate the extrapyramidal effects of metoclopramide.
- Monoamine Oxidase Inhibitors (MAOIs) · May potentiate extrapyramidal effects.
- Opiates · May enhance the hypotensive effects of phenothiazines; dosages may need to be reduced.
- Organophosphate Agents · Phenothiazines should not be given within one month of worming with these agents as their toxic effects may be potentiated.
- CNS Depressants (e.g., opioids, barbiturates, anesthetics) · Additive central nervous system depression and sedation. · major
- Anticholinergic agents (e.g., atropine, glycopyrrolate) · Additive anticholinergic effects (tachycardia, dry mouth, ileus). · moderate
監測
- Clinical efficacy (resolution of vomiting or pruritus)
- Degree of sedation
- Hydration status (if vomiting persists)
- Heart rate and rhythm
- Blood pressure (especially with IV use)
- Level of consciousness / CNS status
- Respiratory rate
過量
Overdose may result in profound sedation, severe hypotension, or acute extrapyramidal clinical signs (e.g., torticollis, tremors, excessive salivation, rigidity). * **Treatment**: Supportive care is primary. Acute extrapyramidal signs have been successfully treated with injectable **diphenhydramine** in humans. Hypotension should be treated with IV fluids; avoid epinephrine due to the risk of epinephrine reversal (use alpha-agonists like phenylephrine if pressors are required).
VetSheet 藥物參考供持牌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方最新藥品說明書。