メチルフェニデート
メチルフェニデートは、構造および薬理学的にアンフェタミンに関連する中枢神経系（CNS）刺激薬です。獣医学においては、主に犬の**ナルコレプシー/カタプレキシー**および**運動亢進症（多動症）**の診断および管理のために適応外使用されます。 中枢神経への作用に加えて、弱い交感神経模倣作用を持ちますが、標準的な治療用量では末梢循環への影響は最小限です。 > **臨床上の注意点**：メチルフェニデートは米国においてスケジュールII（C-II）の規制薬物であり、厳格な処方規制と人間による乱用の高いリスクを伴います。獣医師は処方および調剤の際、適切な法的および倫理的予防措置を講じる必要があります。
作用機序: 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.
動物種別の用量
- 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
用量は獣医療従事者向けの臨床リファレンスです。必ず最新の添付文書と個々の患者で確認してください。
投与経路
禁忌
- Seizure disorders
- Cardiac disease or hypertension
- Aggressive animals
有害事象
- Tachycardia (increased heart rate)
- Tachypnea (increased respiratory rate)
- Anorexia
- Tremors
- Hyperthermia (particularly exercise-induced)
薬物相互作用
- 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
モニタリング
- 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)
過量投与
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 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。