Fenoxibenzamina
Phenoxybenzamine
Phenoxybenzamine HCl
También conocido como: Dibenzyline · Dibenyline · SKF-688A · Dibenzyran · Fenoxene · Phenoxybenzaminum
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 |
|---|---|---|---|---|---|
| Functional urethral obstruction | 0.25 mg/kg | PO | q12-24h | — | 🌎 NA |
| Functional urethral obstruction | 0.25 mg/kg | PO | q12h | — | 🌎 NA |
| Functional urethral obstruction | 0.25-0.5 mg/kg | PO | once or twice daily | — | 🌎 NA |
| Functional urethral obstruction | 5-15 mg (total dose) | PO | q12h | — | 🌎 NA |
| Hypertension associated with pheochromocytoma (pre-surgical) | Initially 0.5 mg/kg, gradually increase every few days until clinical signs of hypotension, adverse reactions, or max dosage of 2.5 mg/kg is attained | PO | twice daily | 1-2 weeks prior to surgery | 🌎 NA |
| Hypertension associated with pheochromocytoma (medical management) | Initial dose 0.25 mg/kg, gradually increase every few days until signs of hypotension, adverse reaction, or max dosage of 2.5 mg/kg is attained | PO | twice daily | Long-term | 🌎 NA |
| Adjunctive treatment of endotoxicosis | 0.25-0.5 mg/kg | PO | q6h | — | 🌎 NA |
- Functional urethral obstruction: Alternative dose: 2.5-20 mg (total dose) PO q12-24h
- Hypertension associated with pheochromocytoma (pre-surgical): Continue until the time of surgery. Close perioperative monitoring is critical.
- Hypertension associated with pheochromocytoma (medical management): Beta-blockers may be added for severe tachycardia, but NEVER without prior alpha-blockade to avoid severe hypertension.
- Adjunctive treatment of endotoxicosis: Use with appropriate antimicrobials, steroids, and supportive care.
Gatos
| Indicación | Dosis | Vía | Frecuencia | Duración | Región |
|---|---|---|---|---|---|
| Functional urethral obstruction | 2.5-7.5 mg/cat | PO | once to twice daily | — | 🌎 NA |
| Functional urethral obstruction | 1.25-7.5 mg (total dose) | PO | q12-24h | — | 🌎 NA |
| Functional urethral obstruction | 2.5-10 mg (total dose) | PO | q24h | — | 🌎 NA |
| Short-term treatment of hypertension | 0.5 mg/kg | PO | q12h | — | 🌎 NA |
| Short-term treatment of hypertension | 2.5 mg (total dose) increasing by 2.5 mg up to a maximum of 10 mg (total dose) | PO | q12h | — | 🌎 NA |
| Short-term treatment of hypertension | 2.5-7.5 mg per cat | PO | q8-12h | — | 🌎 NA |
Caballos
| Indicación | Dosis | Vía | Frecuencia | Duración | Región |
|---|---|---|---|---|---|
| Decrease urethral sphincter tone in bladder paresis | 0.7 mg/kg | PO | 4 times a day | — | 🌎 NA |
| Adjunctive treatment of laminitis (developmental phase) | 1 mg/kg | IV | q12h | for 2 doses | 🌎 NA |
| Treatment of profuse, watery diarrhea | 200-600 mg | — | q12h | — | 🌎 NA |
- Decrease urethral sphincter tone in bladder paresis: Used in combination with bethanechol at 0.25-0.75 mg/kg PO 2-4 times a day.
Las dosis son una referencia clínica para profesionales veterinarios autorizados. Confirme siempre con el prospecto actual y cada paciente individual.
Resumen
La fenoxibenzamina es un antagonista alfa-adrenérgico no competitivo de acción prolongada.
En medicina veterinaria, se utiliza principalmente para:
- Pequeños animales: Reducir el tono del esfínter uretral interno para tratar la obstrucción uretral funcional o la arreflexia del detrusor. También es un medicamento preoperatorio crítico para pacientes con feocromocitoma para prevenir crisis hipertensivas potencialmente mortales durante la manipulación quirúrgica del tumor.
- Equinos: Aplicaciones específicas que incluyen el manejo de la laminitis en etapa temprana, diarreas secretoras y paresia vesical.
Perla clínica: Debido a que la fenoxibenzamina se une de forma irreversible a los receptores, sus efectos son prolongados y solo pueden revertirse mediante la síntesis de nuevos receptores, un proceso que toma varios días.
Mecanismo de acción
Phenoxybenzamine covalently and irreversibly binds to alpha-1 and alpha-2 adrenergic receptors → non-competitive blockade of circulating epinephrine and norepinephrine → profound vasodilation and relaxation of smooth muscle.
- Urinary Tract: Blockade of alpha receptors in the trigone and internal urethral sphincter → decreased urethral resistance → facilitation of bladder emptying.
- Cardiovascular: Blockade of vascular alpha receptors → decreased peripheral vascular resistance → lowered blood pressure (often causing reflex tachycardia).
Because the binding is irreversible, the effect is often described as a 'chemical sympathectomy'. It has no effect on beta-adrenergic or parasympathetic receptors.
Seguridad y advertencias
Contraindicaciones
- Conditions where hypotension is undesirable (e.g., shock, unless fluid replacement is adequate)
- Horses with clinical signs of colic
- Glaucoma (relative contraindication)
- Diabetes mellitus (relative contraindication)
Efectos adversos
- Hypotension (postural/orthostatic)
- Hypertension (rebound)
- Miosis
- Increased intraocular pressure
- Tachycardia (reflex)
- Sodium retention
- Inhibition of ejaculation
- Nasal congestion
- Weakness or dizziness
- Gastrointestinal effects (nausea, vomiting)
- Constipation (specifically noted in horses)
Precauciones
Use with extreme caution in patients with congestive heart failure (CHF) or other heart disease, as drug-induced tachycardia can occur. Use cautiously in patients with renal damage or cerebral/coronary arteriosclerosis.
Pregnancy: FDA Category C. Animal studies (guinea pigs) have shown abnormalities in the closure of the patent ductus. Use only if benefits outweigh risks.
Interacciones farmacológicas
Epinephrine reversal: If used with drugs that have both alpha- and beta-adrenergic effects, increased hypotension, vasodilation, or tachycardia may result due to unopposed beta effects.
Phenoxybenzamine will antagonize the effects of alpha-adrenergic sympathomimetic agents.
Phenoxybenzamine can antagonize the hypothermic effects of reserpine.
Increased risk of first dose hypotensive effect; if used for phaeochromocytoma, beta-blockers must only be started after alpha blockade is in place to avoid hypertensive crisis.
Increased risk of first dose hypotensive effect.
Phenoxybenzamine will antagonize the effects of these agents.
Monitorización
- Clinical efficacy (e.g., adequate urination, ease of voiding)
- Blood pressure (monitor for hypotension)
- Heart rate (monitor for reflex tachycardia)
- Heart rate and rhythm
- Urine output and ease of urination
Farmacocinética
Absorción
Variably absorbed from the GI tract, with a bioavailability of 20-30% in humans. Onset of action is slow (several hours) and increases over several days after regular dosing. Effects persist for 3-4 days after discontinuation.
Distribución
Highly lipid soluble and may accumulate in body fat. Unknown if it crosses the placenta or enters milk.
Metabolismo
Metabolized (dealkylated) in the liver.
Eliminación
Excreted in both the urine and bile.
Sobredosis
Overdosage may yield signs of postural hypotension (dizziness, syncope), tachycardia, vomiting, lethargy, or shock.
Treatment:
- Empty the gut if ingestion was recent and there are no contraindications.
- Treat hypotension with aggressive intravenous fluid support.
- DO NOT USE EPINEPHRINE (causes paradoxical further drop in blood pressure due to unopposed beta-adrenergic vasodilation).
- Most standard vasopressors are ineffective due to the alpha-blockade. Intravenous norepinephrine (levarterenol) may be beneficial if clinical signs are severe.
Productos disponibles
Formulaciones
- Capsules
- 10 mg oral capsule
- 50 mg/ml injectable solution
Etiquetado para humanos
- Phenoxybenzamine HCl Capsules: 10 mg (Dibenzyline)
- Dibenyline 10 mg capsules
- Phenoxybenzamine 50 mg/ml solution
Estado regulador
POM (Prescription Only Medicine)
POM (Prescription Only Medicine)
Sin datos reguladores para: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Almacenamiento y estabilidad
Capsules should be stored at room temperature in well-closed containers.
Información para el cliente
La fenoxibenzamina a menudo se receta para ayudar a su mascota a orinar con mayor facilidad al relajar los músculos del tracto urinario, o para controlar la presión arterial alta asociada con ciertos tumores de las glándulas suprarrenales.
- La paciencia es clave: Puede tomar una semana o más ver el efecto completo en la micción de su mascota. No suspenda el medicamento antes de tiempo a menos que su veterinario se lo indique.
- Administrar con comida: Administrar este medicamento con las comidas puede ayudar a reducir el malestar estomacal (náuseas o vómitos).
- Vigile la presión arterial baja: Debido a que este fármaco relaja los vasos sanguíneos, puede causar una caída en la presión arterial. Comuníquese con su veterinario de inmediato si su mascota parece débil, mareada o se desploma, especialmente después de ponerse de pie.
- Dosis omitida: Si olvida una dosis, adminístrela tan pronto como lo recuerde, pero nunca administre dos dosis a la vez.
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.