Irreversible Non-Selective Alpha Adrenoceptor Antagonist — Phaeochromocytoma Pre-operative Preparation Pregnancy: Use with caution — limited data; phaeochromocytoma in pregnancy requires specialist multidisciplinary management

Phenoxybenzamine

Brand names: Dibenyline

Adult dose

Dose: 10 mg once daily initially; increase by 10 mg every 2 days to achieve BP control (typically 1–2 mg/kg/day in divided doses)

Route: Oral

Frequency: Twice daily (divided)

Max: Titrated to BP response — usually 40–120 mg/day in divided doses

Irreversible alpha blockade — duration determined by receptor turnover (days). Pre-operative: begin 10–14 days before surgery. Target: seated SBP <130/80 mmHg with postural drop <10–20 mmHg. Add beta-blocker only AFTER adequate alpha blockade to prevent unopposed alpha vasoconstriction causing hypertensive crisis.

Paediatric dose

Dose: 0.2 mg/kg mg/kg

Route: Oral

Frequency: Twice daily

Max: Titrated by specialist

BNFc: used in paediatric phaeochromocytoma pre-operative preparation under specialist endocrinology/surgery

Dose adjustments

Renal

Use with caution

Hepatic

Use with caution

Paediatric weight-based calculator

Patient weight (kg)

BNFc: used in paediatric phaeochromocytoma pre-operative preparation under specialist endocrinology/surgery

Clinical pearls

Critical rule: alpha-blockade BEFORE beta-blockade in phaeochromocytoma — beta-blocker alone removes the vasodilatory beta-2 effect, leaving unopposed alpha-mediated vasoconstriction causing hypertensive crisis
Irreversible blockade: recovery requires new receptor synthesis — 3–7 days after stopping; patient will remain alpha-blocked post-operatively requiring IV fluid resuscitation as vasoconstriction returns
Post-operative hypotension: due to loss of phaeochromocytoma-driven vasoconstriction + residual alpha blockade — anticipate large fluid requirements intraoperatively
Selective alpha-1 blockers (doxazosin, prazosin) now used as alternative in many centres — reversible blockade, less postural hypotension; phenoxybenzamine remains gold standard in many endocrine surgery units
Adequate pre-op preparation reduces intraoperative BP swings and mortality significantly

Contraindications

Concurrent alpha-adrenoceptor stimulants
History of cerebrovascular accident (relative)

Side effects

Postural hypotension (prominent)
Reflex tachycardia
Nasal congestion
Miosis
Inhibition of ejaculation
GI upset
Fatigue
Fluid retention (pre-operatively — give IV fluids post-op)

Interactions

Beta-blockers: MUST NOT be started before phenoxybenzamine — unopposed alpha stimulation causes hypertensive crisis; always alpha-block first, then add beta-blocker
Sildenafil and other vasodilators — additive hypotension

Monitoring

Blood pressure (lying and standing)
Heart rate
Pre-operative BP targets (<130/80 mmHg seated, no hypotensive symptoms on standing)
Post-operative fluid balance

Reference: BNFc; BNF 90; Endocrine Society Phaeochromocytoma Guidelines 2014; UK Phaeochromocytoma Guidelines (Specialist Advisory Committee). Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways