Fenobarbital
Phenobarbital
Phenobarbital sodium, phenylethylbarbituric acid, phenylethylmalonylurea
También conocido como: Luminal Sodium · Solfoton · Epiphen · Epityl · Phenoleptil · Fenobarbital · Phenemalum · Phenobarbitalum · Phenobarbitone · Phenylethylbarbituric acid · Phenylethylmalonylurea · Phenobarbital sodium
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 |
|---|---|---|---|---|---|
| Idiopathic epilepsy (initial dose) | 2-2.5 mg/kg | PO | q12h | — | 🌎 NA |
| Idiopathic epilepsy (initial maintenance) | 2.5-3 mg/kg | PO | q12h | — | 🌎 NA |
| Idiopathic epilepsy (rapid loading) | 16-20 mg/kg once IV loading dose, then 2-5 mg/kg PO q12h | IV/PO | Once then q12h | — | 🌎 NA |
| Status epilepticus | 2-5 mg/kg bolus (repeat at 20 min intervals up to 2x), or add to diazepam infusion at 2-10 mg/hour | IV | PRN | — | 🌎 NA |
| Status epilepticus (post-benzodiazepine) | 5-8 mg/kg | IV | q4-6h | — | 🌎 NA |
| Sialadenosis | 1 mg/kg | PO | q12h | 3 months | 🌎 NA |
| Sedation | 2.2-6.6 mg/kg | PO | q12h | — | 🌎 NA |
| Irritable bowel syndrome | 2.2 mg/kg | PO | q12h | — | 🌎 NA |
| Compulsive behaviors (adjunctive) | 2-20 mg/kg | PO | q12-24h | — | 🌎 NA |
- Idiopathic epilepsy (initial dose): Monitor serum concentrations 2-3 weeks after initiating. Target 20-35 mcg/mL.
- Idiopathic epilepsy (initial maintenance): Perform baseline CBC, chem, UA before starting.
- Status epilepticus: If seizures persist after diazepam therapy.
- Status epilepticus (post-benzodiazepine): Continue until seizures are under control.
- Sialadenosis: Slowly weaned off after 3 months.
Gatos
| Indicación | Dosis | Vía | Frecuencia | Duración | Región |
|---|---|---|---|---|---|
| Idiopathic epilepsy (initial dose) | 2-2.5 mg/kg | PO | q12h | — | 🌎 NA |
| Idiopathic epilepsy (maintenance) | 1-2 mg/kg | PO | q12h | — | 🌎 NA |
| Idiopathic epilepsy (rapid loading) | 16-20 mg/kg once IV loading dose, then 1-5 mg/kg PO q12h | IV/PO | Once then q12h | — | 🌎 NA |
| Status epilepticus | 2-5 mg/kg bolus (repeat at 20 min intervals up to 2x), or add to diazepam infusion at 2-10 mg/hour | IV | PRN | — | 🌎 NA |
| Emergency seizure control | 3 mg/kg (repeat q20m up to 24 mg/kg/24h) OR 10 mg/kg bolus | IV | PRN | — | 🌎 NA |
| Sedation (situational distress/travel) | 2-3 mg/kg | PO | PRN | — | 🌎 NA |
- Idiopathic epilepsy (initial dose): Optimum therapeutic levels 23-30 mcg/mL.
- Idiopathic epilepsy (maintenance): Adjust based on serum levels.
- Status epilepticus: If seizures persist after diazepam therapy.
- Emergency seizure control: Given along with IV diazepam.
- Sedation (situational distress/travel): For controlling excessive vocalization.
Hurones
| Indicación | Dosis | Vía | Frecuencia | Duración | Región |
|---|---|---|---|---|---|
| Seizures | 1-2 mg/kg | PO | q8-12h (2-3 times daily) | — | 🌎 NA |
| Seizures (rapid loading) | Loading dose of 16-20 mg/kg once IV; maintenance dose of 1-2 mg/kg PO q8-12h | IV/PO | q8-12h | — | 🌎 NA |
Caballos
| Indicación | Dosis | Vía | Frecuencia | Duración | Región |
|---|---|---|---|---|---|
| Seizures (Adults) | Loading dose of 12 mg/kg IV over 20 minutes, then 6.65 mg/kg IV over 20 minutes q12h | IV | q12h | — | 🌎 NA |
| Seizures (Adults) | Loading dose of 16-20 mg/kg once IV; maintenance dose of 1-5 mg/kg PO twice daily | IV/PO | q12h | — | 🌎 NA |
| Seizures (Foals) | Loading dose of 16-20 mg/kg once IV; maintenance dose of 100-500 mg (total dose) PO twice daily | IV/PO | q12h | — | 🌎 NA |
| Seizures (Foals) | 20 mg/kg diluted and infused over 25-30 minutes IV, then 9 mg/kg infused as above q8h | IV | q8h | — | 🌎 NA |
Ganado
| Indicación | Dosis | Vía | Frecuencia | Duración | Región |
|---|---|---|---|---|---|
| Enzyme induction in organochlorine toxicity | 5 grams | PO | Daily | 3-4 weeks on, 3-4 weeks off, repeat | 🌎 NA |
Las dosis son una referencia clínica para profesionales veterinarios autorizados. Confirme siempre con el prospecto actual y cada paciente individual.
Resumen
El fenobarbital es un barbitúrico de acción prolongada que constituye un pilar en la medicina veterinaria para el manejo de los trastornos convulsivos.
- Uso principal: Se considera ampliamente el fármaco de primera elección para el tratamiento de la epilepsia idiopática en gatos y sigue siendo uno de los medicamentos anticonvulsivos de primera línea o adyuvantes más comunes y eficaces en perros y caballos.
- Ventajas clínicas: Ofrece un perfil farmacocinético favorable, seguridad relativa, eficacia probada y bajo costo. Puede controlar eficazmente las convulsiones a dosis subhipnóticas.
- Autoinducción hepática: Una característica farmacológica única del fenobarbital es su capacidad para inducir las enzimas del citocromo P450 hepático. Con el tiempo, el hígado del paciente se vuelve más eficiente en la metabolización del fármaco, lo que a menudo requiere aumentos de dosis para mantener los niveles séricos terapéuticos.
- Otros usos: Más allá del control de las convulsiones, se utiliza ocasionalmente como sedante oral (p. ej., para la ansiedad por viaje en gatos o vocalización excesiva) y se ha empleado en el manejo del status epilepticus tras el control inicial con benzodiazepinas.
Mecanismo de acción
Phenobarbital exerts its antiseizure and sedative effects through multiple mechanisms within the central nervous system:
- GABA-A Receptor Modulation: Phenobarbital binds to the allosteric barbiturate site on the GABA-A receptor. Unlike benzodiazepines (which increase the frequency of chloride channel opening), phenobarbital increases the duration of chloride channel opening → enhanced influx of chloride ions → hyperpolarization of the postsynaptic neuronal membrane → increased seizure threshold and decreased spread of seizure activity.
- Glutamate Inhibition: It inhibits the release of excitatory neurotransmitters, specifically glutamate, thereby dampening CNS excitability.
- Calcium Channel Blockade: At high (anesthetic) doses, it inhibits the uptake of calcium at nerve endings, further reducing neurotransmitter release.
- Other Neurotransmitters: It has also been shown to inhibit the release of acetylcholine and norepinephrine.
Seguridad y advertencias
Contraindicaciones
- Known hypersensitivity to barbiturates
- Severe liver disease
- Nephritis (large doses)
- Severe respiratory depression
- Hepatic dysfunction
- Severe renal impairment
Efectos adversos
- Dogs: Transient anxiety, agitation, or lethargy upon initiation
- Dogs: Polydipsia (PD), polyuria (PU), and polyphagia (PP)
- Dogs: Sedation and ataxia (especially at higher serum levels)
- Dogs: Elevated liver enzymes (ALT, ALP) - common and not always indicative of failure
- Dogs: Hepatotoxicity (uncommon, usually at levels >30-40 mcg/mL)
- Dogs: Rare blood dyscrasias (anemia, thrombocytopenia, neutropenia)
- Dogs: Rare superficial necrolytic dermatitis (SND)
- Cats: Ataxia, persistent sedation, lethargy
- Cats: Polyphagia, weight gain, PU/PD
- Cats: Rare immune-mediated reactions and bone marrow hypoplasia
- Cats: Coagulopathies (at very high doses)
- Blood dyscrasias (rare)
Precauciones
Intravenous Administration: Must be given SLOWLY (not more than 60 mg/minute). Too rapid IV administration may cause profound respiratory depression.
Tissue Irritation: Do NOT administer subcutaneously (SC) or perivascularly. The injectable solution is highly alkaline and very irritating, potentially causing significant tissue necrosis.
- Patient Conditions: Use with extreme caution in patients that are hypovolemic, anemic, have borderline hypoadrenal function, or have pre-existing cardiac or respiratory disease.
- Feline Sensitivity: Cats are particularly sensitive to the respiratory depressant effects of barbiturates.
- Hepatic Function: Chronic administration induces hepatic microsomal enzymes. Monitor liver function closely, especially in dogs, as hepatotoxicity can occur at high serum concentrations.
- Endocrine Testing: Can alter thyroid testing (decreased T4, normal T3, normal/increased TSH) and may cause a false positive low-dose dexamethasone suppression test.
Interacciones farmacológicas
Increased risk for hepatotoxicity, particularly with large or chronic doses of barbiturates.
Increased risk for hepatotoxicity secondary to carprofen metabolites.
May prolong phenobarbital effects.
Barbiturates may affect phenytoin metabolism, and phenytoin may alter barbiturate levels.
May induce enzymes that increase the metabolism of barbiturates.
Phenobarbital reduces levetiracetam elimination half-life by about 50% in dogs.
Phenobarbital may decrease anticoagulant effects by lowering serum concentrations.
Phenobarbital increases the metabolism and clearance of corticosteroids, potentially reducing their efficacy.
Phenobarbital decreases doxycycline serum concentrations; effect may persist for weeks after discontinuation.
Phenobarbital increases theophylline metabolism, lowering its serum concentrations.
May increase the effects of phenobarbital while phenobarbital may decrease chloramphenicol levels.
Increased hepatic metabolism and clearance of T4
Inhibits phenobarbital metabolism
Monitorización
- Anticonvulsant efficacy (seizure frequency and severity)
- Adverse effects (CNS depression, ataxia, PU/PD, weight gain)
- Serum phenobarbital levels (Dogs: 20-35 mcg/mL; Cats: 23-30 mcg/mL). Wait 5-6 half-lives (12-14 days in dogs, 9-10 days in cats) before measuring steady-state levels.
- Routine CBC, liver enzymes (especially ALT and AST), and bilirubin at least every 6 months during chronic therapy.
- Serum phenobarbital concentrations (trough levels)
- Liver enzymes (ALT, ALP, GGT)
- Serum bile acids
- Complete Blood Count (CBC)
- Renal function
Farmacocinética
Vida media
Absorción
Slowly absorbed from the GI tract. Bioavailability is approximately 90% in dogs and practically complete in adult horses. Peak levels occur 4-8 hours after oral dosing in dogs.
Distribución
Widely distributed throughout the body. Due to lower lipid solubility compared to other barbiturates, it does not distribute as rapidly into the CNS. Protein binding is 40-60%. Volume of distribution: Dogs ~0.75 L/kg, Horses ~0.8 L/kg.
Metabolismo
Metabolized in the liver primarily by hydroxylated oxidation to p-hydroxyphenobarbital; sulfate and glucuronide conjugates are also formed. Induces hepatic microsomal enzymes, leading to auto-induction and increased clearance over time.
Eliminación
Approximately 25% is excreted unchanged by the kidneys. Alkalinizing the urine or increasing urine flow increases excretion rates.
Sobredosis
Clinical Signs of Toxicity:
- Dogs: Ataxia, lethargy, sedation, recumbency, depression, hypothermia, and coma.
- Cats: Ataxia, sedation, and recumbency.
Treatment:
- Decontamination: Removal of ingested product from the gut if recent. Activated charcoal is highly effective and acts as a 'sink' to draw the drug from the vasculature back into the gut, enhancing clearance even if the drug was given parenterally.
- Supportive Care: Provide intensive respiratory and cardiovascular support.
- Enhanced Elimination: Forced alkaline diuresis can substantially augment elimination in patients with normal renal function. Peritoneal dialysis or hemodialysis may be helpful in severe intoxications or anuric patients.
Productos disponibles
Formulaciones
- Tablets
- Capsules
- Oral elixir/suspension
- 12.5 mg oral tablet
- 15 mg oral tablet
- 25 mg oral tablet
- 30 mg oral tablet
- 50 mg oral tablet
- 60 mg oral tablet
- 100 mg oral tablet
- 4% (40 mg/ml) oral solution
- 15 mg/5 ml oral solution
- 15 mg/ml injectable solution
- 30 mg/ml injectable solution
- 60 mg/ml injectable solution
- 200 mg/ml injectable solution
Veterinario
- None currently labeled for veterinary use.
- Epiphen
- Epityl
- Phenoleptil
Etiquetado para humanos
- Phenobarbital Tablets: 15 mg, 16 mg, 30 mg, 60 mg, 90 mg, & 100 mg (Solfoton, generic)
- Phenobarbital Elixir: 15 mg/5mL, 20 mg/5mL (generic)
- Phenobarbital Sodium Injection: 30 mg/mL, 60 mg/mL, 65 mg/mL, & 130 mg/mL (Luminal Sodium, generic)
- Phenobarbital oral solution
Estado regulador
POM-V, POM CD SCHEDULE 3
Sin datos reguladores para: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Almacenamiento y estabilidad
Tablets: Store in tight, light-resistant containers at room temperature (15-30°C); protect from moisture. Elixir: Store in tight containers at 20-25°C. Injection: Store at room temperature (15-30°C). Do not add to acidic solutions or use if precipitate forms.
Información para el cliente
Guía importante para los propietarios de mascotas:
- La constancia es clave: Para un tratamiento exitoso de la epilepsia, debe administrar este medicamento a la misma hora todos los días. Omitir incluso una sola dosis puede desencadenar una convulsión.
- Efectos secundarios iniciales: Al comenzar el medicamento, su mascota puede actuar como si estuviera "ebria" (tambaleante, somnolienta o inusualmente hambrienta/sedienta). Esto es normal y generalmente mejora significativamente después de las primeras 1 a 2 semanas a medida que su cuerpo se ajusta.
- No suspender abruptamente: Nunca deje de administrar este medicamento repentinamente sin consultar a su veterinario, ya que esto puede causar convulsiones graves que ponen en peligro la vida.
- Monitoreo: Su veterinario necesitará extraer sangre periódicamente para verificar los niveles del fármaco en sangre y monitorear la función hepática. Esto es crucial para la seguridad de su mascota y para asegurar que la dosis sea la correcta.
- Seguridad: Mantenga este medicamento estrictamente fuera del alcance de niños y otras mascotas. Guárdelo en un envase a prueba de niños.
- Cuándo llamar al veterinario: Contacte a su veterinario de inmediato si las convulsiones de su mascota no están controladas, si se vuelve extremadamente letárgica o si nota signos como coloración amarillenta en los ojos/encías (ictericia) o debilidad severa.
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.