Drug reference

phenoxybenzamine

Nonselective α adrenergic receptor antagonist (irreversible) · Antihypertensive, Alpha Blocker

Nonselective α adrenergic receptor antagonist (irreversible)Antihypertensive, Alpha BlockerATC C04AB01

CDSCO approvedATC C04AB01

EXCRETION

—

not curated

INTERACTIONS

2 major

SEVERE in our sources

PREGNANCY

—

not curated

Top interactions

AdrenalineSevereTextbookKDT 7e · p60
TizanidineSevereDatabaseDDInter

Mechanism

Phenoxybenzamine is an irreversible α adrenergic receptor antagonist that binds covalently. It causes a progressive decrease in peripheral resistance due to antagonism of α adrenergic receptors in the vasculature and increases cardiac output due to reflex sympathetic stimulation and enhanced norepinephrine release (due to presynaptic α2 blockade).

Indications

pheochromocytomas (preparation for surgery, prolonged treatment for inoperable/malignant)autonomic hyperreflexia (off-label)PheochromocytomaSecondary shockPeripheral vascular disease

Dosing

Adult: 20–60 mg/day oral; 1 mg/kg by slow i.v. infusion over 1 hour

Pharmacokinetics

Bioavailability

Oral absorption is erratic and incomplete

Protein binding

Phenoxybenzamine has an irreversible action.

Metabolism

Chronic administration leads to accumulation in adipose tissue.

Excretion

Most of the administered dose is excreted in urine in 24 hours; small amounts that have covalently reacted remain in tissues for long periods.

Contraindications

abrupt discontinuation (hypertensive crisis)

Side effects

Common

postural hypotensionreflex tachycardiacardiac arrhythmiasreversible inhibition of ejaculationPalpitationNasal blockageMiosisInhibition of ejaculationCNS stimulation (on rapid i.v. injection)Nausea (on rapid i.v. injection)Vomiting (on rapid i.v. injection)Depression (oral doses)Tiredness (oral doses)Lethargy (oral doses)

Serious