Methylphenidate
Methylphenidate is a central nervous system (CNS) stimulant that is structurally and pharmacologically related to amphetamines. In veterinary medicine, it is primarily utilized off-label for the diagnosis and management of **narcolepsy/cataplexy** and **hyperkinesis (hyperactivity)** in dogs. Beyond its CNS effects, it possesses weak sympathomimetic activity but generally has minimal impact on peripheral circulation at standard therapeutic doses. > **Clinical Pearl**: Because methylphenidate is a Schedule II (C-II) controlled substance in the USA, it carries strict prescribing regulations and a significant risk for human diversion and abuse. Veterinarians must exercise appropriate legal and ethical precautions when dispensing.
กลไกการออกฤทธิ์: 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.
ขนาดยาตามชนิดสัตว์
- 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
ขนาดยาเป็นข้อมูลอ้างอิงทางคลินิกสำหรับสัตวแพทย์ผู้มีใบอนุญาต โปรดตรวจสอบกับฉลากล่าสุดและผู้ป่วยแต่ละรายเสมอ
วิธีการให้ยา
ข้อห้ามใช้
- Seizure disorders
- Cardiac disease or hypertension
- Aggressive animals
อาการไม่พึงประสงค์
- Tachycardia (increased heart rate)
- Tachypnea (increased respiratory rate)
- Anorexia
- Tremors
- Hyperthermia (particularly exercise-induced)
อันตรกิริยาระหว่างยา
- 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
การติดตาม
- 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)
การได้รับยาเกินขนาด
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.
ข้อมูลอ้างอิงยาของ VetSheet มีไว้สำหรับสัตวแพทย์ผู้มีใบอนุญาตเพื่อช่วยในการตัดสินใจทางคลินิก ไม่ใช่สิ่งทดแทนการวินิจฉัยของผู้เชี่ยวชาญหรือฉลากล่าสุดของผู้ผลิต