An alpha-blocker for phaeochromocytoma
Phenoxybenzamine
A long-acting alpha-blocker used mainly to control blood pressure before surgery for a phaeochromocytoma.
What is Phenoxybenzamine?
Phenoxybenzamine is a long-acting alpha-blocker used mainly to control blood pressure before surgery to remove a phaeochromocytoma, a rare tumour of the adrenal gland that makes too much adrenaline-like hormone. By blocking the effect of these hormones on blood vessels, it keeps blood pressure under control and makes surgery safer. Because it is powerful and long-acting, it commonly causes a marked drop in blood pressure on standing, a stuffy nose and a fast heartbeat. It is started and supervised by specialists.
Education and reference only. This is a plain-language guide to Phenoxybenzamine — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Phenoxybenzamine is a long-acting medicine in the alpha-blocker family. Its main use is to prepare people for surgery to remove a phaeochromocytoma, a rare tumour (usually of the adrenal gland) that releases large amounts of adrenaline-like hormones and can cause dangerously high blood pressure. By blocking the effect of these hormones on blood vessels, phenoxybenzamine keeps blood pressure steady in the weeks before the operation and reduces the risk of severe blood-pressure surges during it. It is a specialist medicine, started in hospital or under close specialist care.
How it works
Phenoxybenzamine blocks alpha receptors on the muscle in blood vessel walls, and it does so in a long-lasting, hard-to-reverse way. In a phaeochromocytoma, the tumour floods the body with adrenaline-like hormones that clamp blood vessels tight and push blood pressure up. By blocking these receptors, phenoxybenzamine keeps the vessels relaxed and blood pressure controlled, even when surges of hormone occur, which is why it is used to make removal of the tumour safer. Its long-lasting action is useful before surgery but also explains side effects such as a strong drop in blood pressure on standing.
Company & origin
Originated / developed by: Generic (long-established).
A long-acting alpha-blocker used in the UK mainly to control blood pressure before surgery to remove a phaeochromocytoma.
Practical use
How to take Phenoxybenzamine
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it exactly as directed by the specialist team, usually starting low and building up under supervision.
- Stand up slowly, as it commonly causes a marked drop in blood pressure and dizziness on standing.
- Report dizziness, fainting or a very fast heartbeat to your team.
- Follow any advice you are given on drinking enough fluids and on salt, which helps support your blood pressure.
- Do not stop it or change the amount yourself; the team manages it carefully around your surgery.
Weighing it up
Advantages & disadvantages of Phenoxybenzamine
Advantages
- Controls blood pressure before surgery to remove a phaeochromocytoma, making the operation safer.
- Long-acting, so it keeps blood pressure steady even when the tumour releases surges of hormone.
- A well-established treatment for this specific, uncommon situation.
Disadvantages
- Commonly causes a marked drop in blood pressure on standing, with dizziness or fainting.
- Often causes a stuffy nose and a fast or pounding heartbeat.
- A powerful, long-acting medicine that must be started and supervised by specialists.
Practical use
Good to know
This is a specialist medicine for an uncommon situation, started and supervised by hospital teams. Because it is powerful and long-acting, it very commonly causes a marked fall in blood pressure when you stand up, which can make you feel dizzy or faint, so it is important to stand up slowly and report dizziness. A blocked or stuffy nose and a fast or pounding heartbeat are also common, and the fast heartbeat is sometimes managed with a second medicine added after phenoxybenzamine has been started. In men it can reduce ejaculation. It must be handled and given carefully, and you should follow the specialist team's instructions closely, including any advice on staying well hydrated and on salt intake to support your blood pressure.
Who should not take it / use with caution
- It is generally avoided in people who have recently had a heart attack or stroke, or who have certain circulation problems.
- It must be used with great care, and only under specialist supervision, in older people and those with heart disease.
- It is reserved for specific specialist situations rather than ordinary high blood pressure.
Monitoring
- Close monitoring of blood pressure, including standing blood pressure, before surgery.
- Checking heart rate, as a fast heartbeat may need an extra medicine.
- Specialist review of fluid balance and readiness for the operation.
Side effects
- A marked drop in blood pressure on standing, causing dizziness, light-headedness or fainting.
- A blocked or stuffy nose and a fast or pounding heartbeat are common.
- Tiredness, dry mouth and, in men, reduced ejaculation; rarely, more serious heart-rhythm effects.
Key interactions
- Other blood-pressure-lowering medicines add to its blood-pressure-lowering effect.
- A type of medicine called a beta-blocker is sometimes added, but only after phenoxybenzamine, to control fast heartbeat.
- Medicines that raise blood pressure may be made less effective, which matters around surgery and anaesthesia.
Available as: Capsules taken by mouth, and a solution given by drip in hospital in some situations.
Answers
Phenoxybenzamine: frequently asked questions
What is phenoxybenzamine used for?
It is used mainly to control blood pressure before surgery to remove a phaeochromocytoma, a rare adrenal-gland tumour that releases too much adrenaline-like hormone.
Why do I feel dizzy when I stand up?
It commonly causes a marked drop in blood pressure on standing. Stand up slowly and report dizziness or fainting to your specialist team.
Why has my nose become stuffy?
A blocked or stuffy nose is a common effect of phenoxybenzamine because of the way it relaxes blood vessels, and it usually settles.
Why might I need another medicine for my heart rate?
It can cause a fast heartbeat, which is sometimes controlled by adding a beta-blocker, but only after phenoxybenzamine has been started.
Can I manage it myself at home?
It is a specialist medicine started and supervised by hospital teams. Take it exactly as directed and do not change the amount yourself.
Authoritative sources
- BNF
- NICE CKS
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