Dosing and uses of Dibenzyline (phenoxybenzamine)
Adult dosage forms and strengths
capsule
- 10mg
Hypertension Pheochromocytoma
10 mg PO BID initially; increase qOD to 20-40 mg PO BID/TID (sometimes higher doses necessary)
Bladder Management (Off-label)
Initial 10 mg PO qD; can be increased q5d by 10 mg PO q8-12hr
Other Indications & Uses
Off-label: Raynaud's phenomenon, overactive bladder (neurogenic, prostatic obstruction), shock, hypertensive emergencies d/t epinephrine
Pediatric dosage forms and strengths
capsule
- 10mg
Pheochromocytoma Hypertension (Off-label)
0.25-1 mg/kg PO qD; increase to effect slowly; not to exceed 10 mg/day
Dibenzyline (phenoxybenzamine) adverse (side) effects
Frequency not defined
Orthostatic hypotension
Tachycardia
Dizziness
Drowsiness
Fatigue
Malaise
Sedation
Dry mouth
Nausea
Vomiting
Inhibition of ejaculation
Miosis
Nasal congestion
Warnings
Contraindications
Hypersensitivity to phenoxybenzamine
Any conditions in which fall in BP is undesirable
Orthostatic hypotension
Cautions
Cerebral or coronary arteriosclerosis, CHF, respiratory infection, renal impairment
Concomitant use of drugs that stimulate alpha/beta receptors (may incr hypotension/tachycardia)
May have carcinogenic potentiaL
First dose effect may occur, causing a sudden and drastic fall in blood pressure after administering the first dose.
Hypotension/syncope may occur with first few doses or with increase in dose
Minimize by using small first dose at bedtime
Increase dose slowly
Pregnancy and lactation
Pregnancy category: C
Lactation: Not known if excreted into breast milk, discontinue drug or do not nurse
Pregnancy categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA: Information not available.
Pharmacology of Dibenzyline (phenoxybenzamine)
Half-Life: 24 hr
Onset: several hours
Duration: several days
Bioavailability: 20-30%
Metabolism: extensively metabolized in liver
Metabolite: N-phenoxyisopropyl-benzylamine
Excretion: urine & feces
Mechanism of action
Alpha blocker, noncompetitive alpha-adrenergic blockade of post ganglionic synapses in smooth muscle, exocrine glands
