派醋甲酯 / 甲基芬尼達
派醋甲酯（Methylphenidate）是一種中樞神經系統（CNS）興奮劑，其結構和藥理作用與安非他命相似。在獸醫學中，主要用於標示外使用（off-label use），以診斷和控制犬隻的**猝睡症/猝倒症（narcolepsy/cataplexy）**及**過動症（hyperkinesis）**。 除了中樞神經作用外，它具有微弱的擬交感神經活性，但在標準治療劑量下對周邊循環的影響極小。 > **臨床要點**：由於派醋甲酯在美國屬於第二級（C-II）管制藥品，具有嚴格的處方規定以及極高的人類濫用風險。獸醫師在開立處方和配藥時，必須採取適當的法律與道德防範措施。
作用機制: Methylphenidate acts primarily as a **norepinephrine-dopamine reuptake inhibitor (NDRI)**. * It binds to and blocks the **dopamine transporter (DAT)** and **norepinephrine transporter (NET)** on presynaptic neurons. * Blockade of these transporters → prevents the reuptake of monoamines → increases the concentration of **dopamine** and **norepinephrine** in the extraneuronal space (synaptic cleft). * This amplified monoamine signaling in the brainstem arousal system and cerebral cortex leads to increased alertness, focus, and CNS stimulation.
各物種劑量
- Treatment of narcolepsy/cataplexy · 5-10 mg (total dose) · PO · once daily
- Treatment of narcolepsy/cataplexy (to supplement imipramine) · 0.25-0.5 mg/kg or 5-10 mg (total dose) · PO · q12-24h · Used to supplement imipramine given at 0.5-1 mg/kg PO q8-12h
- Diagnosis and treatment of hyperkinesis · 5-20 mg (total dose) · PO · q8-12h · 3 days · Give for 3 days and assess for improvement of target behaviors (anxiety, overactivity, learning ability)
- Hyperkinesis-hyperactivity · Small dogs: 5+ mg total dose; Large Dogs: 20-40 mg total dose · PO · q12h
劑量為持牌獸醫專業人員的臨床參考。請務必對照最新藥品說明書及個別病患確認。
給藥途徑
禁忌症
- Seizure disorders
- Cardiac disease or hypertension
- Aggressive animals
不良反應
- Tachycardia (increased heart rate)
- Tachypnea (increased respiratory rate)
- Anorexia
- Tremors
- Hyperthermia (particularly exercise-induced)
藥物相互作用
- Anticonvulsants (phenobarbital, primidone, phenytoin) · Methylphenidate may increase serum levels of these anticonvulsants
- Clonidine · Rare cases of cardiovascular effects (including death) reported in humans; mechanism unknown
- Hypotensive drugs · Methylphenidate may reduce the efficacy of hypotensive effects
- MAO Inhibitors (amitraz, selegiline) · Concurrent use could lead to a severe hypertensive crisis
- SSRI Antidepressants (fluoxetine, sertraline) · Methylphenidate may inhibit SSRI metabolism and increase their serum levels
- Tricyclic Antidepressants (amitriptyline, clomipramine) · Methylphenidate may inhibit TCA metabolism and increase their serum levels
- Warfarin · Methylphenidate may inhibit warfarin metabolism and increase INR
監測
- Clinical efficacy (improvement in target behaviors or narcoleptic episodes)
- Vital signs (heart rate, respiratory rate)
- Body weight (monitor for anorexia/weight loss)
- Periodic CBC with differential and platelet counts (recommended during prolonged therapy based on human guidelines)
過量
Toxicity can occur at relatively low doses in veterinary patients. * **Dogs**: Doses of 1 mg/kg (or below) can cause toxic reactions. One fatality was reported at 3.1 mg/kg, though research dogs have survived 20 mg/kg/day for 90 days. * **Cats**: A 5 mg tablet caused severe toxicity (tremors, agitation, mydriasis, tachycardia, tachypnea, hypertension) which resolved after 25 hours with supportive care. **Clinical Signs of Overdose**: Primarily CNS over-stimulation and excessive sympathomimetic effects: hyperactivity, salivation, diarrhea, head bobbing, agitation, tachycardia, hypertension, tremors, seizures, and hyperthermia. **Treatment**: * **Decontamination**: Standard gut detoxification (emesis, activated charcoal, cathartic). *Avoid emesis if the animal is already symptomatic* due to seizure/aspiration risks. * **Supportive Care**: * **Phenothiazines** (e.g., acepromazine, chlorpromazine) to control agitation. * **Beta-blockers** to manage severe tachycardia. * **External cooling** for hyperthermia. * **Cyproheptadine** may be administered to help prevent or treat serotonin syndrome.
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。