doxazosin
Meaning of doxazosin: One receptor sits in two very different places, which is how a single tablet ended up treating both blood pressure and prostate symptoms.
Definition of doxazosin
Doxazosin is a medicine that blocks alpha-1 adrenergic receptors, the switches through which nerve signals keep smooth muscle contracted. Blocking them relaxes muscle in the walls of arteries and in the prostate and bladder neck. The first effect lowers blood pressure by widening vessels; the second eases the urinary difficulty caused by an enlarged prostate.
What are its two uses?
| Use | What relaxes | Result |
|---|---|---|
| High blood pressure | Muscle in the walls of arteries | Vessels widen and resistance to blood flow falls |
| Enlarged prostate | Muscle in the prostate and the neck of the bladder | Urine passes more freely, with less straining and urgency |
The two uses look unrelated but rest on the same receptor sitting in two places. In the prostate the benefit does not depend on the gland shrinking at all: the muscle within it simply stops squeezing the urethra, so relief appears within days. That is the opposite of the drugs that block the hormone driving prostate growth, which shrink the gland slowly over months. As an alpha blocker, doxazosin also has a specialized role in preparing someone for surgery on an adrenaline-producing adrenal tumor, where the receptors must be blocked before the tumor is handled.
Why is the first dose different?
Standing up drops blood toward the legs, and the body answers by tightening those vessels within a second or two. An alpha blocker blunts exactly that reflex. Blood pools, pressure at the head falls, and the result is lightheadedness or, less often, a faint. The effect is strongest with the very first dose and after each increase, before the circulation has adjusted, which is why treatment starts at a low dose, rises slowly, and is often taken at bedtime. Palpitations may accompany it as the heart speeds up to compensate. Alpha blockers are also linked to a floppy iris during cataract surgery, which is why an eye surgeon is told the drug is being taken.
Is it a first choice for blood pressure?
No longer. A large trial comparing treatments for high blood pressure stopped its doxazosin arm early after more heart failure appeared in that group than among those taking a diuretic. Since then alpha blockers have been kept as an added agent rather than a starting one, used when other classes have not brought pressure down or when prostate symptoms make the double effect useful. In prostate enlargement their position is unchanged and they remain a mainstay. The same molecule is also sold as doxazosin mesylate, which is the salt form rather than a different drug.
Also known as
Used in a sentence
Doxazosin was prescribed to help manage both the patient's blood pressure and urinary symptoms related to prostate enlargement.
Good to know
Doxazosin lowers blood pressure most sharply after the first dose and after each increase in dose, an effect that can cause lightheadedness or fainting on standing because the reflex that normally tightens blood vessels is blunted.