Phenoxybenzamine

DIBENZYLINE

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Pronunciation: fen-ox-ee-BEN-za-meen

Phenoxybenzamine ballicule: receptor binding, kinetics and half-life diagram — Mechanism of action: Phenoxybenzamine ballicule

What it isIrreversible non-selective alpha antagonist; preoperative blockade in phaeochromocytoma.

Why this oneIrreversible blockade cannot be overcome by a catecholamine surge, which is exactly what is needed during tumor handling.

What limits itReflex tachycardia and profound orthostasis; a beta blocker must not be started first. The effect persists for days after stopping.

Phenoxybenzamine molecular structure (skeletal formula) — Molecular structure: Phenoxybenzamine

Phenoxybenzamine prescription history

Animated chart of estimated U.S. prescriptions per year, Antihypertensives (1953–2026). Phenoxybenzamine enters in 1953 (estimated).

FDA-approved for

pheochromocytoma (~1953)

Principal riskReflex tachycardia and profound orthostasis

Classes and tags

Clinical profile

Therapeutic safety burden1 / 4

Overdose danger1 / 4

Weight-gain liability0 / 4

Sedation liability0 / 4

QT / Torsades0 / 4

Direct muscarinic antagonism0 / 4

Embryofetal risk1 / 4

Legacy pregnancy categoryUnknown / historical label unavailable

Defining liabilityGenerally tolerated at therapeutic doses; clinically important risks are agent-specific and increase with interactions or organ impairment.

FDA label

Read the full label on DailyMed ↗

NO BOXED WARNINGS

FDA dosing	Population	Start	Target	Max
Pheochromocytoma (control of hypertension and sweating episodes)	Adults	10 mg BID	20–40 mg BID–TID (titrated to BP control)	Undefined

Titration Every other day

Renal Undefined

Hepatic Undefined

Long-term use not recommended (carcinogenicity). Add a beta-blocker if tachycardia is excessive.

Available strengths

cap 10 mg

Contraindications

Conditions where a fall in blood pressure may be undesirable

Cautions

Unopposed beta stimulation: mixed alpha/beta agonists may cause exaggerated hypotension and tachycardia

Adverse reactions

Postural hypotension
Tachycardia
Inhibition of ejaculation
Nasal congestion
Miosis
GI irritation
Drowsiness
Fatigue

Pregnancy No adequate animal reproduction studies; unknown fetal risk — use only if clearly needed.

Lactation Unknown whether excreted in milk; discontinue nursing or drug.

Cost

Phenoxybenzamine (DIBENZYLINE)

Strength		#/mo	generic $/mo	CostPlus
10 mg	cap	60 BID		offered

NADAC is a voluntary CMS survey of what retail community pharmacies pay for the drugs they stock. Phenoxybenzamine is dispensed outside retail pharmacies, so it rarely appears on surveyed invoices.

Generic entry2012

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Self-check

Phenoxybenzamine: Why can a catecholamine surge not overcome its blockade?
The blockade is irreversible.
Phenoxybenzamine: Which blocker must not be started first?
A beta blocker.