Phenoxybenzamine

Where is Phenoxybenzamine used?

Phenoxybenzamine is a prescription used to treat high blood pressure caused by an adrenal tumor called pheochromocytoma. This is in the class of drugs called alpha-blockers. This relaxes and widens blood vessels so that blood can flow more easily. Each medicine comes as a capsule for oral use.

How does Phenoxybenzamine work?

A pheochromocytoma is a type of tumor of the adrenal gland that causes high blood pressure. It is because the tumor produces excessive amounts of the hormones adrenaline and noradrenaline. These hormones act on alpha-adrenergic receptors that are found on the walls of blood vessels that cause blood vessels to contract and narrow. Phenoxybenzamine works by opposing the action of the hormones produced by the tumor. It blocks the alpha receptors in the blood vessel walls. In that way, it stops adrenaline and noradrenaline from acting on them. This allows the blood vessels to relax and widen which lets the blood pass more easily through the blood vessels.

There is a slow onset of drug action that takes several hours which increases over several days after regular dosing. The effects of this medication persist for 3 to 4 days after discontinuation of the drug.

How is Phenoxybenzamine taken?

You must take this medication exactly as it is given by your doctor. You should not take less or more often than the prescription. Your doctor may direct you to start at a lower dose and eventually increase it.

Phenoxybenzamine is to be taken by mouth usually 2 to 3 times a day or as directed. You may take each dose with or without food. It is important to continue taking this even if you feel well. To help you remember, take it at the same time and in the same way each day. Drink plenty of fluids while having this treatment.

What are the possible side effects of Phenoxybenzamine?

Common side effects:

  • Stomach upset
  • Nausea
  • Drowsiness
  • Dizziness
  • Stuffy nose
  • Lack of energy
  • Headache
  • Dryness of mouth
  • Tired feeling
  • Light-headedness especially when getting up from a lying or sitting position

What are the precautions in taking Phenoxybenzamine?

  • Phenoxybenzamine may occasionally cause your blood pressure to drop when you move from a lying down or sitting position. This may make you dizzy and may rarely cause fainting. To avoid this, carefully move from lying down to sitting and try getting up slowly. If you feel dizzy, sit or lie down until the symptoms pass.
  • This medicine may cause fatigue. Be careful when performing potentially dangerous activities such as driving. Do it until you know how this medicine affects you.
  • This is not recommended for use in pregnancy unless considered essential by your doctor.
  • If you are a breastfeeding women, consult your doctor first before using this drug.
  • Limit alcoholic beverages while having this medication.
  • Inform your doctor if you have current medications including herbal supplements and vitamins.
  • Do not share this or any of your medications with others even if they have the same symptoms as yours.
  • You should not take a dose of this drug if you are allergic to it. Let your doctor know right away before using Phenoxybenzamine.