Phenoxybenzamine

Indications
 Oral
Hypertension in phaeochromocytoma
Adult: As hydrochloride: Initially, 10 mg once or bid. Gradually increase, as necessary, to 1-2 mg/kg daily in 2 divided doses.
Child: Initially, 0.2 mg/kg (max: 10 mg) once daily. Increase by 0.2 mg/kg increments. Maintenance dose: 0.4-1.2 mg/kg/day every 6-8 hr; higher doses may be required.
Oral
Urinary retention
Adult: As hydrochloride: 10 mg bid.
Intravenous
Operative cover in patients with phaeochromocytoma
Adult: As hydrochloride: 1 mg/kg daily in 200 ml sodium chloride 0.9% infused over at least 2 hr.
Intravenous
Severe shock
Adult: As hydrochloride: 1 mg/kg daily in 200-500 ml sodium chloride 0.9% infused over at least 2 hr.
Contraindications
 Conditions in which fall in BP would be dangerous.
Warnings / Precautions
 Heart failure, ischaemic heart disease, cerebrovascular disease, renal impairment. Porphyria. Pregnancy and lactation. Discontinue use if angina develops or worsens. Respiratory tract infections. Elderly.
Adverse Reactions
 Nasal congestion, slight GI irritation, miosis, postural hypotension with dizziness, fatigue, compensatory tachycardia, inhibition of ejaculation, dry mouth, decreased sweating, confusion, drowsiness, convulsions (rapid IV infusion).
Overdose Reactions
 Symptoms: Hypotension, tachycardia, lethargy, dizziness, shock. Management: Treat hypotension and shock by postural measures and parenteral fluid volume replacement. Do not use epinephrine.
Drug Interactions
 May antagonise the effects of α-adrenergic stimulating agents. Increased toxicity with β-blockers. Alcohol ingestion may exaggerate hypotensive effects.
Potentially Fatal: Cardiac-accelerating and hypotensive effects may be enhanced by epinephrine and other drugs that stimulate both α- and β-adrenergic receptors. Additive hypotensive effects with sildenafil, tadalafil, vardenafil.
See Below for More phenoxybenzamine Drug Interactions
Mechanism of Actions
 Phenoxybenzamine produces an irreversible (non-competitive) blockade by binding covalently to α-receptors in the smooth muscle.
Onset: Gradual over several hr (oral).
Duration: 3-4 days (oral/IV).
Absorption: Incompletely and variably absorbed from the GI tract (oral).
Metabolism: Hepatic.
Excretion: Via urine and bile. Plasma half-life: 24 hr (IV).
Storage Conditions
 Oral: Store at 25°C (77°F).
ATC Classification
 C04AX02 - phenoxybenzamine ; Belongs to the class of other peripheral vasodilators.
Storage
 Oral: Store at 25°C (77°F).
Available As
  • Phenoxybenzamine 10 mg
  • Phenoxybenzamine 50 mg

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