alpha-blocker
Meaning of alpha-blocker: Named for the receptor it occupies, this drug group loosens smooth muscle so vessels widen and urine flows more easily.
Definition of alpha-blocker
An alpha-blocker is a medicine that settles onto alpha receptors and stops adrenaline reaching them. Smooth muscle in artery walls and around the bladder outlet then relaxes instead of tightening. The group is used mainly for the urinary symptoms of an enlarged prostate, and for blood pressure that has not come down on other treatments.
What is the difference between alpha-1 and alpha-2?
Alpha receptors come in two families. Alpha-1 receptors sit on the smooth muscle of arteries, the prostate and the bladder neck, and switching them off is what produces the useful effects. Alpha-2 receptors sit mostly on nerve endings, where they act as a brake on further release of noradrenaline. Blocking those releases more noradrenaline instead of less, which is why the newer drugs are built to leave alpha-2 alone. The prostate-selective members go further still and aim at the receptor subtype concentrated in the urinary tract.
How does it differ from a beta-blocker?
| Alpha-blocker | Beta-blocker | |
|---|---|---|
| Receptor blocked | Alpha, mainly on smooth muscle | Beta, mainly on the heart and airways |
| Main effect | Vessels widen, bladder outlet relaxes | Heart slows and beats less forcefully |
| Typical use | Prostate symptoms, resistant blood pressure | Angina, irregular rhythm, heart failure |
| Common drawback | Dizziness on standing | Fatigue, cold hands, wheeze in asthma |
How does it compare with the prostate-shrinking drugs?
Two different classes treat the same urinary problem in opposite ways. An alpha-blocker relaxes the muscle inside the gland, so the stream improves in days, but the prostate is exactly the size it was. A 5-alpha-reductase inhibitor lowers the hormone signal that keeps the gland growing, so the gland slowly shrinks over months. The two are often combined, since one gives quick relief and the other addresses the bulk.
What are the drawbacks?
Light-headedness on standing is the effect people notice most, and it is strongest at the start. Nasal stuffiness, tiredness and headache occur. Many men on the prostate-selective drugs find that semen no longer emerges at climax, because the same valve mechanism has been relaxed. This is harmless and reverses when the drug stops. Cataract surgeons need to know about current or past use, because the iris becomes floppy and behaves unpredictably during the operation. The term alpha-adrenergic antagonist means the same thing.
Also known as
Used in a sentence
An alpha-blocker was prescribed first, with a 5-alpha-reductase inhibitor added later for the enlarged gland.
Good to know
Alpha-blockers relax the prostate without changing its size, so the improvement in urine flow arrives within days but stops as soon as the drug is stopped.