Fenitoína sódica
Phenytoin Sodium
Diphenylhydantoin
También conocido como: Dilantin · Phenytek · Diphenylhydantoin · DPH · Fenitoina · Phenantoinum · Phenytoinum
Revisado por el equipo veterinario de VetSheetActualizado 5 abr 2026Referencia veterinaria basada en la evidencia
Las dosis son una referencia clínica para profesionales veterinarios autorizados. Confirme siempre con el prospecto actual y cada paciente individual.
Dosis por especie
🌎 NA — North America🌍 EU — Europe
Perros
| Indicación | Dosis | Vía | Frecuencia | Duración | Región |
|---|---|---|---|---|---|
| Treatment of seizures | 15-40 mg/kg | PO | three times daily | — | 🌎 NA |
| Treatment of seizures | 20-35 mg/kg | PO | three times daily | — | 🌎 NA |
| Treatment of seizures | 8.8-17.6 mg/kg in divided doses | PO | divided doses | — | 🌎 NA |
| Treatment of ventricular arrhythmias | Up to 10 mg/kg in increments of 2-4 mg/kg OR 20-35 mg/kg | IV or PO | three times daily (for PO) | — | 🌎 NA |
| Treatment of ventricular arrhythmias | 10 mg/kg slowly IV; 30-50 mg/kg PO | IV, PO | q8h (for PO) | — | 🌎 NA |
| Treatment (or prophylaxis) of digitalis intoxication | 50 mg/kg | PO | q8h | — | 🌎 NA |
| Treatment of hypoglycemia secondary to tumor | 6 mg/kg | PO | two to three times daily | — | 🌎 NA |
- Treatment of seizures: 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.
- Treatment (or prophylaxis) of digitalis intoxication: Long-term use may cause increases in serum alkaline phosphatase and increased hepatic cell size.
Gatos
| Indicación | Dosis | Vía | Frecuencia | Duración | Región |
|---|---|---|---|---|---|
| Treatment of ventricular arrhythmias | 2-3 mg/kg | PO | q24h | — | 🌎 NA |
| Treatment of seizures | 2-3 mg/kg daily; 20 mg/kg per week | PO | daily or weekly | — | 🌎 NA |
- Treatment of ventricular arrhythmias: Diligent monitoring is required due to accumulation risk.
- Treatment of seizures: Use is very controversial in this species.
Caballos
| Indicación | Dosis | Vía | Frecuencia | Duración | Región |
|---|---|---|---|---|---|
| Seizures | 2.83-16.43 mg/kg | PO | q8h | — | 🌎 NA |
| Digoxin induced arrhythmias | 10-22 mg/kg | PO | q12h | — | 🌎 NA |
| 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 | — | 🌎 NA |
- Seizures: To obtain serum levels from 5-10 micrograms/mL. Suggest monitoring serum levels to adjust dosage.
- Digoxin induced arrhythmias: Adverse effects are muscle fasciculations and sedation.
- Treatment of ventricular dysrhythmias: For persistent ventricular extra systoles or ventricular tachycardia where conventional treatment has failed. Suggest monitoring plasma concentrations.
Las dosis son una referencia clínica para profesionales veterinarios autorizados. Confirme siempre con el prospecto actual y cada paciente individual.
Resumen
La fenitoína sódica es un anticonvulsivo derivado de la hidantoína y un agente antiarrítmico de Clase IB. Aunque es históricamente significativa en medicina humana, su uso en medicina veterinaria está altamente restringido debido a perfiles farmacocinéticos desfavorables en animales de compañía.
- Perros: Rara vez se utiliza para el manejo de la epilepsia a largo plazo debido a una vida media muy corta y a una rápida autoinducción hepática, lo que hace que mantener niveles séricos terapéuticos sea casi imposible sin una administración frecuente y en dosis altas.
- Gatos: Altamente susceptibles a la acumulación tóxica debido a una vida media severamente prolongada (hasta 108 horas) y a deficiencias en las vías de glucuronidación.
- Nicho clínico: Hoy en día, se reserva principalmente para el tratamiento de arritmias ventriculares inducidas por digoxina en perros y caballos, o condiciones neuromusculares raras específicas (p. ej., mioquimia y neuromiotonía en gatos).
Nota clínica: Debido a su capacidad para inhibir la secreción de insulina, se ha investigado como tratamiento coadyuvante para la hipoglucemia secundaria a insulinomas, aunque los beneficios clínicos suelen ser mínimos.
Mecanismo de acción
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).
Seguridad y advertencias
Contraindicaciones
- Hypersensitivity to phenytoin or other hydantoins
- Intravenous use is contraindicated in 2nd or 3rd degree heart block
- Sinoatrial block
- Adams-Stokes syndrome
- Sinus bradycardia
Efectos adversos
- 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)
Precauciones
Hepatotoxicity Warning: Chronic therapy in dogs requires regular monitoring of liver function due to the risk of hepatocellular hypertrophy, necrosis, and hepatic lipidosis.
- Pregnancy: Potentially teratogenic (FDA Category D / Papich Class C). It readily crosses the placenta and is excreted in maternal milk. Use only when benefits clearly outweigh risks.
- Feline Sensitivity: Cats metabolize phenytoin extremely slowly. Use is highly controversial and requires diligent monitoring to prevent severe toxicity.
- IV Administration: Must be given slowly. Rapid IV injection can cause severe hypotension and cardiac arrhythmias.
Interacciones farmacológicas
Significantly increases the serum half-life of phenytoin (e.g., from 3 to 15 hours in dogs) by inhibiting its hepatic metabolism.
The toxicity of lithium may be enhanced.
Phenytoin may decrease the analgesic properties of meperidine but enhance its toxic effects.
Altered pharmacologic effects; potential for additive hepatotoxicity. Weigh risks vs. benefits before combining.
May increase the pharmacologic effects and toxicity of phenytoin.
May decrease the pharmacologic activity of phenytoin.
Phenytoin may decrease the pharmacologic activity of these agents via hepatic enzyme induction.
Monitorización
- 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)
Farmacocinética
Vida media
Absorción
Nearly completely absorbed in humans, but in dogs, oral bioavailability may only be about 40%.
Distribución
Well distributed throughout the body. About 78% bound to plasma proteins in dogs (vs. 95% in humans). Protein binding may be reduced in uremic patients. Readily crosses the placenta and small amounts are excreted into milk.
Metabolismo
Metabolized in the liver; much of the drug is conjugated to a glucuronide form. Phenytoin induces hepatic microsomal enzymes, enhancing the metabolism of itself (autoinduction) and other drugs.
Eliminación
Excreted by the kidneys as metabolites.
Sobredosis
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).
Productos disponibles
Formulaciones
- Extended-release capsules: 30 mg, 100 mg, 200 mg, 300 mg
- Oral suspension: 25 mg/mL
- Chewable tablets: 50 mg
- Injection: 50 mg/mL
Veterinario
- None currently available
Etiquetado para humanos
- Phenytoin Sodium Extended-Release Capsules: 30 mg, 100 mg, 200 mg & 300 mg (Dilantin Kapseals, Phenytek)
- Phenytoin Oral Suspension: 25 mg/mL (Dilantin-125)
- Phenytoin Tablets: 50 mg chewable (Dilantin Infa-Tabs)
- Phenytoin Sodium Injection: 50 mg/mL (46 mg/mL phenytoin base)
Estado regulador
Sin datos reguladores para: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Almacenamiento y estabilidad
Store capsules at room temperature (below 86°F) and protect from light and moisture. Store injection at room temperature and protect from freezing. If injection is frozen/refrigerated, a precipitate may form which should resolubilize when warmed. Do not use precipitated solutions. Injectable solutions will precipitate at a pH less than 11.5.
Información para el cliente
- Horario estricto: Administre este medicamento exactamente como se le recetó. Omitir dosis puede provocar crisis convulsivas o ritmos cardíacos peligrosos.
- Administración: Administrar el medicamento con comida puede mejorar la absorción y disminuir el malestar estomacal.
- Vigile los efectos secundarios: Notifique a su veterinario inmediatamente si su mascota se muestra extremadamente letárgica, pierde el apetito, vomita o parece tambaleante/ebria (atáxica).
- Salud dental: En perros, este fármaco puede causar crecimiento excesivo de las encías (hiperplasia gingival). Los chequeos dentales regulares y una buena higiene oral son importantes.
-
Advertencia de seguridad: Nunca comparta medicamentos humanos con su mascota. La forma en que los animales procesan este fármaco es muy diferente a la de los humanos, y una dosificación incorrecta puede ser fatal.
La referencia de medicamentos de VetSheet está destinada a profesionales veterinarios autorizados como ayuda para la toma de decisiones clínicas, no como sustituto del criterio profesional ni del prospecto actual del fabricante.