Non-selective irreversible α-blocker Pregnancy: Adequate reproductive studies in animals have not been performed and it is not known whether phenoxybenzamine hydrochloride can cause fetal harm when given to a pregnant woman. It should be given to a pregnant woman only if clearly needed.

Phenoxybenzamine hydrochloride

Brand names: Dibenyline

A non-selective, irreversible alpha-adrenoceptor blocker used principally for the preoperative control of blood pressure in patients with phaeochromocytoma.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Initially 10 mg twice a day; increase every other day, usually to 20 mg to 40 mg 2 or 3 times a day, until optimal dosage is obtained as judged by blood pressure control

Route: Oral (capsules)

Frequency: Twice daily initially, then 2 or 3 times a day

No UK SPC (eMC) in the bundle — figures are from US prescribing information for phenoxybenzamine hydrochloride capsules (Amneal Pharmaceuticals NY LLC, label date 2026-07-03). This is ORAL CAPSULE labelling only: it does not cover any intravenous/infusion phenoxybenzamine preparation, so if this page is intended to describe IV use the regimen must be sourced separately. Titration principle: the dosage should be adjusted to fit the needs of each patient — small initial doses should be slowly increased until the desired effect is obtained or the side effects from blockade become troublesome, and after each increase the patient should be observed at that level before instituting another increase. Dosage should be carried to a point where symptomatic relief and/or objective improvement are obtained, but not so high that side effects from blockade become troublesome. No numeric maximum dose is stated in the source. Long-term use of phenoxybenzamine is not recommended (see the label's Carcinogenesis and Mutagenesis precautions). Paediatric: safety and effectiveness in paediatric patients have not been established.

Dose auto-extracted from US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Conditions where a fall in blood pressure may be undesirable
Hypersensitivity to phenoxybenzamine hydrochloride capsules or to any of their components

Side effects

Postural hypotension
Tachycardia
Inhibition of ejaculation
Nasal congestion
Miosis
Gastrointestinal irritation, drowsiness and fatigue

Interactions

Compounds that stimulate both alpha- and beta-adrenergic receptors (e.g. adrenaline/epinephrine) — may produce an exaggerated hypotensive response and tachycardia
Levarterenol (noradrenaline) — phenoxybenzamine blocks its hyperthermia production
Reserpine — phenoxybenzamine blocks its hypothermia production

Clinical monograph

How it works

It produces a long-lasting, non-competitive blockade of alpha-1 and alpha-2 adrenoceptors, counteracting the vasoconstriction caused by catecholamine excess.

Prescribing in practice

Alpha blockade must be established before any beta-blocker is added in phaeochromocytoma, otherwise unopposed alpha stimulation can precipitate a hypertensive crisis.
It commonly causes marked postural hypotension, reflex tachycardia and nasal congestion, and its effect is prolonged because the blockade is irreversible.
Adequate dosing requires careful uptitration to control paroxysms and to allow volume expansion before surgery.

Monitoring

Monitor lying and standing blood pressure and heart rate during titration and in the perioperative period.

Counselling the patient

Rise slowly from sitting or lying because of the risk of dizziness and fainting.
A blocked nose and a fast heartbeat are expected effects of the medicine.
Take it as directed in the run-up to your operation and do not stop suddenly.

Evidence & guidelines

Preoperative alpha blockade is the cornerstone of phaeochromocytoma management in endocrine guidelines, with beta blockade added only after adequate alpha blockade.

Reference: UK Endocrine Society; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways