alpha-adrenergic antagonist
Meaning of alpha-adrenergic antagonist: A drug class that occupies the receptors adrenaline uses to squeeze blood vessels and the muscle at the bladder outlet.
Definition of alpha-adrenergic antagonist
An alpha-adrenergic antagonist is a drug that blocks alpha receptors, the docking points adrenaline and noradrenaline use to make smooth muscle contract. With the receptor occupied, blood vessel walls relax and the pressure inside them falls, while the muscle around the prostate and bladder neck loosens so urine flows more freely. Prazosin, doxazosin and tamsulosin belong to this group.
What does blocking an alpha receptor do?
Adrenaline and noradrenaline are the body's alarm chemicals. When they land on alpha receptors, smooth muscle tightens: vessels narrow, blood pressure rises, and the ring of muscle at the base of the bladder grips shut. A drug that sits on the receptor without activating it leaves that signal unread. Vessels stay wider, so pressure drops. The bladder outlet stays looser, so a stream that had become weak improves within days rather than months.
What is the class used for?
| Use | What the drug is doing |
|---|---|
| Urinary symptoms of an enlarged prostate | Relaxing muscle in a benign but obstructing gland |
| Blood pressure that has not settled on other drugs | Widening arteries to lower resistance |
| Preparation before removal of a pheochromocytoma | Shielding the circulation from a surge of adrenaline |
| Nightmares in post-traumatic stress disorder | Damping alpha signaling in the brain, an established off-label use |
| Passing a small stone in the ureter | Relaxing the muscle of the lower urinary tract |
Why does the first dose need care?
The same relaxation that lowers high blood pressure can allow blood to pool in the legs on standing, so the brain is briefly short of supply. Dizziness or fainting after an early dose is a known effect, strongest with the older members of the class. Treatment therefore starts small and builds. The prostate-selective drugs act mainly on the receptor subtype in the urinary tract, so they disturb blood pressure less. One further effect matters to eye surgeons: these drugs slacken the iris, which can complicate cataract surgery long after the last dose. Alpha-adrenergic antagonist and alpha-blocker are two names for the identical class.
Also known as
Used in a sentence
An alpha-adrenergic antagonist was added for urinary symptoms attributed to prostate enlargement.
Good to know
Alpha-adrenergic antagonist and alpha-blocker name the same class, and the slackening of the iris these drugs cause can persist well after the medicine has been stopped, which is why cataract surgeons ask about past use.
Word origin
Where “alpha-adrenergic antagonist” comes from
Adrenergic comes from the Latin ad, meaning near, and ren, meaning kidney, after the adrenal glands sitting on top of them. Antagonist is from the Greek antagonistes, an opponent.