メトクロプラミド
メトクロプラミドは、獣医療において広く使用されている**消化管運動機能改善剤**および**制吐剤**です。 * **消化管運動促進作用**：主に上部消化管（胃および小腸）に作用し、結腸への影響は最小限です。胃うっ滞、胃食道逆流症、術後イレウスに臨床使用されます。 * **制吐作用**：犬は化学受容器引き金帯（CRTZ）にドパミン受容体が豊富にあるため、非常に有効です。逆に猫はD2受容体が少ないため、猫における制吐剤としての信頼性は低くなります（マロピタントなどのNK-1拮抗薬が好まれることが多いです）。 **臨床のポイント**： * パルボウイルス性腸炎や急性膵炎などの重篤な状態に対して、持続静脈内点滴（CRI）として投与されることがよくあります。 * 血液脳関門を通過するため、特に高用量や馬などの感受性の高い動物種において、顕著な錐体外路症状（振戦、落ち着きのなさ、狂乱行動など）を引き起こす可能性があります。
作用機序: 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.
動物種別の用量
- 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
投与経路
禁忌
- 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
有害事象
- 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
薬物相互作用
- 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.
モニタリング
- 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)
過量投与
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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