Phenoxybenzamine is an irreversible, non-selective alpha-blocker. It partially blocks the body’s 5-HT, histaminergic and cholinergic receptors. It is lipid-soluble and can penetrate the brain to produce CNS stimulation.
Mechanism of action.
- The drug cyclizes spontaneously in the body giving rise to a highly reactive ethyleniminium intermediate which reacts with α adrenoceptors and other biomolecules by forming strong covalent bonds.
Clinical uses.
- Bladder management.
- Hypertension Pheochromocytoma.
- Peripheral vascular disease.
Adverse effects.
- Nausea and vomiting on rapid intravenous injection.
- Depression, tiredness, and lethargy.
- Postural hypotension and palpitation.
- Nasal blockage and miosis.
- Inhibition of ejaculation.
- Chronic administration leads to accumulation in the adipose tissue.
Drug interaction.
- Vardenafil increases the effects of phenoxybenzamine by pharmacodynamic synergism.
- Phenoxybenzamine and acebutolol increase anti-hypertensive channel blocking and should be closely monitored.
Contraindication.
· Hypersensitivity to the drug.
· Orthostatic hypotension.
Dosage.
- 20–60 mg/day oral; 1 mg/kg by slow i.v. Infusion over 1 hour; used primarily in pheochromocytoma, occasionally in secondary shock and peripheral vascular disease.
- FENOXENE 10 mg cap, 50 mg/ml injection.
- BIOPHENOX 50 mg in 1 ml injection.
