phenoxybenzamine (Dibenzyline)

Introduction

Tradename: Dibenzyline.

Indications

• prevention or control of paroxysmal hypertension & sweating in patients with pheochromocytoma
• Raynaud's syndrome
• micturition disorders

Contraindications

Caution:

• renal insufficiency
• coronary or cerebral atherosclerosis
• severe congestive heart failure

pregnancy category = c

safety in lactation = ?

Dosage

• adults:
  • start 10 mg PO BID
  • usual maintenance dose: 10-40 mg BID-TID
  • maximum dose: 120 mg/day
• children:
  • 0.2 mg//kg (max 10 mg) QD
  • increase by 0.2 mg/kg increments
  • usual maintenance dose: 0.4-1.2 mg/kg/day divided TID
  • maximum single dose 10 mg

Tabs: 10 mg.

Pharmacokinetics

• well absorbed orally
• onset of action within 2 hours
• peak effect in 4-6 hours
• alpha-adrenergic receptor blockade is complete & may last several days
• highly lipid soluble; accumulates in fat tissue
• elimination 1/2life is 24 hours
• eliminated in bile & urine

Adverse effects

• common (> 10%)
  • nasal congestion, miosis, postural hypotension, tachycardia, dizziness
• less common (1-10%)
  • confusion, dry mouth, headache, sexual dysfunction, tiredness, weakness, syncope, shock, lethargy, nausea/vomiting, diarrhea
• other
  • drowsiness
  • nasal congestion
  • anorgasmia

• drug adverse effects of alkylating agents
• drug adverse effects of antihypertensive agents

Drug interactions

• alcohol in combination increases hypertension
• alpha-adrenergic antagonists block effects of phenoxybenzamine

• drug interaction(s) of NSAIDs & antihypertensives

Mechanism of action

• non-competitive alpha adrenergic receptor antagonist
• peripheral vasodilation
• reflex tachycardia
• blocks & reverses pressor effects of epinephrine
• blocks, but does NOT reverse pressor effects of norepinephrine

More general terms

• alpha adrenergic receptor antagonist
• amine
• alkylating agent
• serotonin antagonist

Database

• PubChem: http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=4768
• PubChem: http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=6141
• PubChem: http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=5284441
• PubChem: http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=657233