26 January 2011

Alpha blockers A-Z

Alpha blockers inhibit the effect of norepinephrine, a hormone that causes constriction of blood vessels.


What is it and how does it work?
Alpha blockers inhibit the effect of norepinephrine, a hormone that causes constriction of blood vessels. By relaxing the muscles in the walls of the blood vessels, arteries dilate and blood pressure decreases.

A few Alpha Blockers

  • Prazosin in Minipress
  • Terazosin in Hytrin
  • Doxazosin in Cardura or Cardura XL

Who benefits from Alpha Blockers?
Alpha blockers may improve urinary flow in men with partial obstruction due to an enlarged prostate.

It seems that alpha blockers slightly increases HDL-cholesterol, and may lower total cholesterol and triglycerides. This may be an advantage to patients with blood fat abnormalities.

Alpha blockers may be of benefit in some patients with glucose intolerance.

However the role of alpha blockers in hypertension is not established and may worsen heart failure in a controlled trial. They are fourth or fifth line drugs, and should generally be used by specialists only. They may have a role in treatment of hypertension in kidney disease, and are drugs of choice for hypertension due for phaeochromocytoma. In patients with prostate problems and hypertension, alpha blockers should not be used primarily for the treatment of their hypertension. Short-acting alpha blockers should be avoided and long-acting drugs like Cardura XL should be preferentially used.

How to take Alpha Blockers
These drugs may cause a sharp drop in blood pressure, especially the first dose. This could lead to dizziness or fainting on standing. This is especially the case with short acting drugs like prazosin, which may cause dangerous falls in the elderly, and should be avoided. This side effect is uncommon with long acting drugs.

Who should not take Alpha Blockers?

  • Patients with postural hypotension – when blood pressure falls on standing, causing dizziness or fainting.
  • Safety in pregnancy is not established.

Possible side effects

  • Orthostatic hypotension, where blood pressure falls on standing. This problem seems to be worse in elderly patients.
  • Headaches, dry mouth and nasal congestion

Possible drug interactions?
Alcohol may increase the adverse effects of these drugs. Combination with calcium channel blockers alone is not advised.

Written by Dr Kathleen Coetzee, MBChB

Reviewed by Prof Brian  Rayner, head of the division of nefhrology and hypertension,University of Cape Town and Groote Schuur Academic Hospital, December 2010

Read more:
Am I at risk for hypertension?


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