Primidona
Primidone
5-ethyldihydro-5-phenyl-4,6(1H,5H)-pyrimidinedione
También conocido como: Mysoline · Neurosyn · hexamidinum · primaclone · primidonum · Cyral · Epidona · Liskantin · Mylepsinum · Prysoline · Resimatil · Sertan
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 |
|---|---|---|---|---|---|
| Seizure control | 10-30 mg/kg per day divided into 2-3 doses | PO | divided into 2-3 doses | — | 🌎 NA |
| Seizure control | 10 mg/kg | PO | q8h | — | 🌎 NA |
- Seizure control: Initially
- Seizure control: Not recommended as first choice
Gatos
| Indicación | Dosis | Vía | Frecuencia | Duración | Región |
|---|---|---|---|---|---|
| Seizure control | 20 mg/kg | PO | q12h | — | 🌎 NA |
- Seizure control: Extreme caution advised; many consider contraindicated in cats.
Las dosis son una referencia clínica para profesionales veterinarios autorizados. Confirme siempre con el prospecto actual y cada paciente individual.
Resumen
La primidona es un anticonvulsivo derivado de los barbitúricos que actúa principalmente como profármaco, convirtiéndose rápidamente en fenobarbital y feniletilmalonamida (PEMA) en perros.
Aunque históricamente se ha utilizado para el control de convulsiones (epilepsia idiopática, convulsiones epileptiformes) en perros, la mayoría de los neurólogos veterinarios ya no recomiendan su uso como agente de primera línea.
Perla clínica: La mayor incidencia de hepatotoxicidad grave asociada con la primidona en comparación con el fenobarbital es el principal factor limitante para la terapia a largo plazo.
En perros, la tasa de conversión de primidona a fenobarbital es de aproximadamente 4:1 (una dosis de 250 mg de primidona es aproximadamente equivalente a 60 mg de fenobarbital). Algunos clínicos reservan la primidona para casos refractarios donde el fenobarbital por sí solo es insuficiente, teorizando que el metabolito PEMA puede potenciar la actividad anticonvulsiva del fenobarbital. Se considera altamente tóxica para gatos y conejos.
Mecanismo de acción
Primidone and its active metabolites, phenylethylmalonamide (PEMA) and phenobarbital, exert anticonvulsant effects by raising seizure thresholds and altering seizure patterns.
Mechanistic Pathway:
- Phenobarbital (Primary active metabolite): Binds to the allosteric barbiturate site on GABA_A receptors in the CNS → prolongs the duration of chloride channel opening → increases intracellular chloride influx → hyperpolarizes the postsynaptic neuron → globally depresses CNS excitability and raises the seizure threshold.
- PEMA: Has weak intrinsic anticonvulsant activity but is believed to synergistically potentiate the effects of phenobarbital.
- Primidone (Parent drug): May have some independent action on voltage-gated sodium channels, though its primary efficacy in veterinary species is attributed to its phenobarbital metabolite.
Seguridad y advertencias
Contraindicaciones
- Severe liver disease
- Demonstrated previous hypersensitivity to primidone or barbiturates
- Nephritis (large doses contraindicated)
- Severe respiratory dysfunction (large doses contraindicated)
- Cats (considered contraindicated by many clinicians due to high toxicity risk)
Efectos adversos
- Anxiety and agitation (especially during initiation)
- Elevated liver enzymes (ALT, ALP, GLDH)
- Decreased serum albumin
- Hepatic lipidosis
- Hepatocellular hypertrophy and necrosis
- Extramedullary hematopoiesis
- Depression and sedation
- Ataxia
- Polydipsia (PD)
- Polyuria (PU)
- Polyphagia
- Anorexia
- Tachycardia
- Dermatitis
- Episodic hyperventilation
- Urolith formation (primidone uroliths reported)
- Megaloblastic anemia (rare)
Precauciones
Species Warnings: Use with extreme caution, if at all, in cats. Primidone is considered highly toxic to felines.
Patient Conditions: Use cautiously in patients who are hypovolemic, anemic, have borderline hypoadrenal function, or have cardiac or respiratory disease.
Drug Transition: When converting dogs from primidone to phenobarbital, it is suggested to do this slowly (tapering 1/4 of the dose each month) to prevent withdrawal seizures.
Laboratory Interference: Barbiturates may cause falsely elevated bromosulfophthalein (BSP) retention. Primidone/phenobarbital can alter thyroid testing (decreased total and free T4, normal T3, normal/increased TSH); wait at least 4 weeks after discontinuation to perform thyroid testing. May cause a false-positive low-dose dexamethasone suppression test.
Interacciones farmacológicas
Increased risk for hepatotoxicity, particularly with large or chronic doses of barbiturates.
Oral administration may decrease the GI absorption of primidone.
May prolong phenobarbital effects.
Barbiturates may affect phenytoin metabolism, and phenytoin may alter barbiturate levels; therapeutic monitoring indicated.
May induce enzymes that increase the metabolism of barbiturates.
May increase the CNS depressant effects of phenobarbital.
May increase the effects of phenobarbital; phenobarbital may also decrease chloramphenicol levels.
May increase the CNS depressant effects of phenobarbital.
May increase the effects of phenobarbital; phenobarbital may decrease phenothiazine serum concentrations.
May increase the effects of phenobarbital.
Phenobarbital may decrease anticoagulant effects by lowering serum concentrations.
Phenobarbital may decrease effects by lowering serum concentrations.
Phenobarbital may decrease effects by lowering serum concentrations.
Phenobarbital may decrease effects by lowering serum concentrations.
Phenobarbital may decrease effects by lowering serum concentrations (effect may persist for weeks after barbiturate is discontinued).
Phenobarbital may decrease effects by lowering serum concentrations.
Monitorización
- Anticonvulsant efficacy (seizure frequency and severity)
- Adverse effects (CNS depression, PU/PD, weight gain, signs of liver disease)
- Serum phenobarbital levels (therapeutic range in dogs thought to be 15-40 mcg/mL) if lack of efficacy or adverse reactions are noted
- Routine CBCs and liver enzyme panels at least every 6 months during chronic therapy
Farmacocinética
Vida media
Absorción
Slowly absorbed after oral administration in the dog, with peak levels occurring 2-4 hours after dosing. Bioavailability in humans is reported as 60-80%.
Distribución
Appears in maternal milk in substantial quantities.
Metabolismo
Rapidly converted to phenylethylmalonamide (PEMA) and phenobarbital in the dog. Induces hepatic microsomal enzymes, increasing the rate of metabolism of itself and other drugs.
Eliminación
Eliminated primarily via hepatic metabolism to active metabolites, which are subsequently cleared.
Sobredosis
Clinical Signs: Because primidone is rapidly metabolized to phenobarbital in dogs, signs of acute toxicity mirror barbiturate overdose: sedation progressing to coma, anorexia, vomiting, ataxia, and nystagmus.
Treatment:
- Decontamination: Removal of ingested product from the gut if appropriate (emesis or gastric lavage).
- Adsorbents: Activated charcoal is of considerable benefit in enhancing the clearance of phenobarbital (acts as a 'sink' for the drug to diffuse from the vasculature back into the gut), even if the drug was administered parenterally.
- Supportive Care: Provide respiratory and cardiovascular support.
- Enhanced Elimination: Forced alkaline diuresis can 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
- Oral suspension
Veterinario
- Primidone Tablets: 50 mg and 250 mg (Neurosyn®)
Etiquetado para humanos
- Primidone Tablets: 50 mg and 250 mg (Mysoline®, generic)
Estado regulador
Sin datos reguladores para: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Almacenamiento y estabilidad
Tablets should be stored in well-closed containers, preferably at room temperature. Oral suspension should be stored in tight, light-resistant containers at room temperature; avoid freezing. Commercially available products generally have a 5-year expiration date.
Información para el cliente
Crucial para el éxito: El cumplimiento estricto de la terapia es esencial para el tratamiento exitoso de la epilepsia. Administre el medicamento exactamente a la misma hora todos los días.
- Cambios de comportamiento: Su perro puede parecer ansioso, agitado o inusualmente somnoliento al comenzar este medicamento. Estos efectos suelen ser temporales y pueden resolverse a medida que su cuerpo se ajusta.
- Aumento de sed/apetito: Puede notar que su mascota bebe, orina y come más de lo habitual. Controle su peso y hable con su veterinario sobre el manejo de la dieta.
- Cuándo llamar al veterinario: Comuníquese con su veterinario de inmediato si su mascota desarrolla letargo severo, pérdida de apetito, vómitos, coloración amarillenta de los ojos/encías (ictericia), encías pálidas o si las convulsiones no están bien controladas.
- No suspenda abruptamente: Nunca deje de administrar este medicamento repentinamente sin orientación veterinaria, ya que esto puede desencadenar convulsiones graves que ponen en peligro la vida.
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.