甲氧氯普胺 (胃復安)
甲氧氯普胺在獸醫學中是一種廣泛使用的**胃腸促動力藥**和**止吐藥**。 * **促動力作用**：主要作用於上消化道（胃和小腸），對結腸的影響極小。臨床上用於胃排空遲緩、胃食道逆流和術後腸阻塞。 * **止吐作用**：由於犬的化學受體觸發區 (CRTZ) 含有豐富的多巴胺受體，因此對犬非常有效。相反，貓的 D2 受體較少，使得甲氧氯普胺在貓身上的止吐效果較不可靠（通常首選 alpha-2 拮抗劑或 NK-1 拮抗劑如 maropitant）。 **臨床要點**： * 常以連續靜脈輸注 (CRI) 的方式用於嚴重疾病，如犬小病毒腸炎或急性胰臟炎。 * 由於它能穿過血腦屏障，可能會引起顯著的錐體外系副作用（例如震顫、焦躁不安、狂亂行為），特別是在高劑量或對此藥敏感的物種（如馬）中。
作用機制: Metoclopramide exerts its effects through both peripheral gastrointestinal and central nervous system mechanisms: * **Peripheral (GI Tract)**: Sensitizes upper GI smooth muscle to **acetylcholine** → increases tone and amplitude of gastric contractions, relaxes the pyloric sphincter, and increases duodenal and jejunal peristalsis. It also increases lower esophageal sphincter (LES) pressure, reducing reflux. * **Central (CNS)**: Antagonizes **Dopamine (D2)** receptors in the **Chemoreceptor Trigger Zone (CRTZ)** → blocks emetic signaling to the vomiting center, providing a potent central antiemetic effect. * **Additional Mechanisms**: At higher doses, it exhibits weak **5-HT3 (Serotonin)** receptor antagonism and **5-HT4** receptor agonism, further contributing to its antiemetic and prokinetic profiles.
各物種劑量
- As a prokinetic for adjunctive treatment of esophagitis · 0.2-0.4 mg/kg PO q8h · PO · q8h · Cisapride considered superior.
- General use · 0.2-0.4 mg/kg PO, SC 3-4 times daily; or as a continuous IV infusion (1-2 mg/kg per day) · PO/SC/IV · tid-qid or CRI
- General use · 0.2-0.5 mg/kg q8h PO or parenterally (may be given as a constant rate IV infusion at 0.01-0.02 mg/kg/hr) · PO/IV/IM/SC · q8h or CRI
- To increase bladder contractility · 0.2-0.5 mg/kg PO q8h · PO · q8h
- To induce milk let-down for secondary agalactia · 0.1-0.2 mg/kg SC q12h · SC · q12h · Used to promote milk production.
- To stimulate the gastrointestinal tract · 0.04 mg/kg/hr as a CRI · IV · CRI · ARCI UCGFS Class 4 Drug.
- For reflux esophagitis · 0.02-0.1 mg/kg SC q4-12 hours · SC · q4-12h · Horses may be prone to extrapyramidal neurologic side effects.
- General therapeutics (Rabbits) · 0.2-1 mg/kg PO or SC q6-8h · PO/SC · q6-8h
- To assist in removing gastric hairballs (Rabbits) · 0.5 mg/kg PO once a day (up to three times a day) · PO · sid to tid
給藥途徑
禁忌症
- GI hemorrhage
- GI obstruction or perforation
- Hypersensitivity to metoclopramide
- Seizure disorders (relatively contraindicated, lowers seizure threshold)
- Head trauma
- Pheochromocytoma (may induce hypertensive crisis)
- Concurrent phenothiazine therapy
- Dogs with pseudopregnancy (stimulates prolactin release)
- Gastrointestinal obstruction
- Gastrointestinal perforation
- Gastrointestinal hemorrhage
- Seizure disorders (epilepsy)
- Pheochromocytoma
不良反應
- Dogs: Changes in mentation and behavior (motor restlessness, involuntary spasms, aggression, hyperactivity to drowsiness/depression), constipation
- Cats: Frenzied behavior, disorientation, constipation
- Horses: Severe CNS effects (IV use), alternating sedation and excitement, behavioral changes, abdominal pain
- Extrapyramidal effects (tremors, rigid posture)
- Nausea and diarrhea
- Transient hypertension
- Elevated prolactin levels
- Extrapyramidal signs (tremors, twitching, hyperactivity, restlessness)
- Sedation
- Constipation or diarrhea
- Changes in mentation or behavior
藥物相互作用
- Aspirin, Acetaminophen, Alcohol · Metoclopramide may enhance the absorption of these agents.
- Anesthetics · Acute hypotension has been reported if metoclopramide is used concurrently IV.
- Atropine (and anticholinergics) · May antagonize the GI motility effects of metoclopramide.
- Cephalexin · Oral metoclopramide increases cephalexin peak plasma concentrations and AUC in dogs.
- Cholinergic Drugs (e.g., bethanechol) · May enhance metoclopramide's GI effects.
- CNS Depressants · Metoclopramide may enhance CNS depressant effects. · moderate
- Cyclosporine · Metoclopramide increases the rate and extent of GI absorption.
- Opiate Analgesics · May antagonize the GI motility effects and enhance metoclopramide's CNS effects.
- MAO Inhibitors (e.g., amitraz, selegiline) · Could cause hypertension.
- Phenothiazines and Butyrophenones · May potentiate the extrapyramidal effects of metoclopramide.
- Propofol · Reduces induction requirements of propofol by 20-25%.
- SSRI Antidepressants · Potential for enhanced extrapyramidal effects.
- Tetracyclines · Metoclopramide increases the rate and extent of GI absorption.
監測
- Clinical efficacy (resolution of vomiting, improved GI transit)
- Adverse effects (especially CNS and extrapyramidal signs)
- Clinical response (reduction in vomiting, improved gastric emptying)
- Hydration status and electrolyte balance
- Signs of extrapyramidal adverse effects (twitching, restlessness)
過量
The oral LD50 doses are very high (465-870 mg/kg in laboratory animals), making death from oral overdose unlikely in veterinary patients. **Clinical Signs of Toxicity**: * Sedation, ataxia, agitation * Extrapyramidal effects (tremors, rigidity, spasms) * Nausea, vomiting, constipation **Treatment**: * No specific antidote exists. * If ingestion was recent, empty the stomach using standard protocols. * **Anticholinergic agents** that enter the CNS (e.g., **diphenhydramine** at 2.2 mg/kg IV, or benztropine) are highly effective in controlling extrapyramidal effects. * Peritoneal dialysis or hemodialysis is not effective for drug removal.
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