페니토인 나트륨

항경련제, 항부정맥제 (Class IB)

**페니토인 나트륨(Phenytoin sodium)**은 히단토인 유도체 항경련제이자 Class IB 항부정맥제입니다. 인의에서는 역사적으로 중요한 약물이지만, 반려동물에서는 약동학적 특성이 불리하여 수의학적 사용이 매우 제한적입니다. - **개**: 반감기가 매우 짧고 간 효소의 빠른 자가유도(autoinduction)가 일어나, 잦은 고용량 투여 없이는 치료 혈청 농도를 유지하기가 거의 불가능하므로 장기적인 간질 관리에 거의 사용되지 않습니다. - **고양이**: 반감기가 심각하게 연장(최대 108시간)되고 글루쿠론산 포합 경로가 결핍되어 있어 독성 축적에 매우 취약합니다. - **임상적 활용**: 현재는 주로 개와 말에서 **디곡신 유발성 심실 부정맥**을 치료하거나, 고양이의 특정 희귀 신경근 질환(예: 근파동증 및 신경근긴장증)에 제한적으로 사용됩니다. **임상 팁**: 인슐린 분비를 억제하는 능력이 있어 인슐린종에 속발하는 저혈당증의 보조 치료제로 연구된 바 있으나, 임상적 이점은 대개 미미합니다.

작용 기전: Phenytoin exhibits both neurological and cardiac effects through the stabilization of excitable membranes: - **Neurological**: Binds to and prolongs the inactive state of **voltage-gated sodium channels (VGSCs)** → promotes sodium efflux and limits sodium influx → stabilizes neuronal membranes and prevents the high-frequency repetitive firing necessary for seizure propagation from epileptogenic foci. - **Cardiac**: Acts as a **Class IB antiarrhythmic** (similar to lidocaine) → slightly depresses phase 0 of the cardiac action potential and shortens phase 3 repolarization → decreases overall action potential duration. It is particularly effective against digitalis-induced arrhythmias. - **Endocrine**: Inhibits the secretion of **insulin** and **vasopressin (ADH)**.

동물 종별 용량

Cats

Treatment of ventricular arrhythmias · 2-3 mg/kg · PO · q24h · Diligent monitoring is required due to accumulation risk.
Treatment of seizures · 2-3 mg/kg daily; 20 mg/kg per week · PO · daily or weekly · Use is very controversial in this species.

Horses

Seizures · 2.83-16.43 mg/kg · PO · q8h · To obtain serum levels from 5-10 micrograms/mL. Suggest monitoring serum levels to adjust dosage.
Digoxin induced arrhythmias · 10-22 mg/kg · PO · q12h · Adverse effects are muscle fasciculations and sedation.
Treatment of ventricular dysrhythmias · 20 mg/kg initially for the first 3-4 doses, followed by a maintenance dose of 10-15 mg/kg · PO · q12h · For persistent ventricular extra systoles or ventricular tachycardia where conventional treatment has failed. Suggest monitoring plasma concentrations.

Dogs

Treatment of seizures · 15-40 mg/kg · PO · three times daily
Treatment of seizures · 20-35 mg/kg · PO · three times daily
Treatment of seizures · 8.8-17.6 mg/kg in divided doses · PO · divided doses · Gradually increase or decrease dose to maintain control. May take several days for seizure control. Note: Unlikely to attain necessary serum levels due to fast half-life.

투여 경로

POIV

금기

Hypersensitivity to phenytoin or other hydantoins
Intravenous use is contraindicated in 2nd or 3rd degree heart block
Sinoatrial block
Adams-Stokes syndrome
Sinus bradycardia

이상반응

Dogs: Anorexia, vomiting, ataxia, sedation, gingival hyperplasia, hepatotoxicity (elevated ALT, decreased albumin, hepatic lipidosis)
Cats: Ataxia, sedation, anorexia, dermal atrophy syndrome, thrombocytopenia
Horses: Excitement, recumbency (at high plasma concentrations)

약물 상호작용

Chloramphenicol · Significantly increases the serum half-life of phenytoin (e.g., from 3 to 15 hours in dogs) by inhibiting its hepatic metabolism.
Lithium · The toxicity of lithium may be enhanced.
Meperidine · Phenytoin may decrease the analgesic properties of meperidine but enhance its toxic effects.
Phenobarbital / Primidone · Altered pharmacologic effects; potential for additive hepatotoxicity. Weigh risks vs. benefits before combining.
Allopurinol, Cimetidine, Diazepam, Isoniazid, Salicylates, Sulfonamides, Trimethoprim, Valproic Acid · May increase the pharmacologic effects and toxicity of phenytoin.
Antacids, Barbiturates, Calcium, Folic Acid, Theophylline · May decrease the pharmacologic activity of phenytoin.
Corticosteroids, Doxycycline, Estrogens, Furosemide, Quinidine · Phenytoin may decrease the pharmacologic activity of these agents via hepatic enzyme induction.

모니터링

Level of seizure control or arrhythmia resolution
Signs of toxicity (sedation, ataxia)
Body weight (monitor for anorexia)
Liver enzymes (ALT, ALP) and serum albumin (especially with chronic therapy)
Serum drug levels (if signs of toxicity appear or lack of efficacy is noted)

과용량

Clinical signs of overdosage are dose-dependent: - **Lower levels**: Sedation, anorexia, and ataxia (wobbly gait). - **Higher levels**: Coma, severe hypotension, and respiratory depression. **Treatment**: Dogs rapidly clear the drug, so treatment depends on the severity of clinical signs. Severe intoxications require aggressive supportive care (IV fluids, cardiovascular and respiratory support).

VetSheet 약물 레퍼런스는 면허 수의 전문가를 위한 임상 의사결정 보조 도구이며, 전문적 판단이나 제조사의 최신 라벨을 대신하지 않습니다.