Doxazosin
A long-acting alpha-1 blocker used for urinary symptoms of an enlarged prostate (BPH) and for high blood pressure.
Drug card
- Class
- Alpha-1 blocker
- How it works
- Blocking alpha-1 receptors, relaxing blood vessels and prostate muscle
- Used for
- Urinary symptoms of an enlarged prostate (BPH)
- High blood pressure
- Known for
- Dizziness, especially on standing
- Fainting after the first dose or a dose increase
- Its name
- -azosin means an alpha-1 blocker (prazosin type)
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does doxazosin work?
A quinazoline that selectively blocks postjunctional alpha-1 receptors, relaxing both blood vessels and the smooth muscle of the prostate and bladder neck. With a half-life of about 22 hours it is taken once a day. In men with normal blood pressure treated for BPH it lowers pressure very little.
Like other alpha-1 blockers: They block alpha-1 adrenergic receptors on smooth muscle, so norepinephrine can no longer contract it. In arterioles and veins this lowers peripheral resistance and blood pressure; in the prostate, its capsule and the bladder neck the muscle relaxes and urine flows more easily. Tamsulosin favors the alpha-1A subtype that dominates the prostate and is not used for blood pressure.
Uses
What is doxazosin used for?
- Urinary symptoms of an enlarged prostate (BPH)
- High blood pressure
Side effects
Side effects of doxazosin
- Dizziness, especially on standingKnown for
- Fainting after the first dose or a dose increaseKnown forSerious
- Tiredness and malaise
- Drowsiness
- Swollen ankles, feet and legs (edema)
- Headache
- Runny or blocked nose
- Breathlessness
- Palpitations
- Floppy iris syndrome during cataract surgery
- Low white cell count
- PriapismSerious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Fainting is most likely after the first dose or a dose increase, and other blood pressure drugs add to the fall.
- PDE5 inhibitors and strong CYP3A4 inhibitors deepen the fall in blood pressure.
- Before cataract surgery, tell the surgeon: floppy iris syndrome can complicate the operation.
- Check for prostate cancer before treating BPH and at intervals afterwards.
Good to know: Unlike tamsulosin it lowers blood pressure, so one drug can treat both BPH and hypertension; unlike prazosin it lasts long enough to be taken once a day.
Remember it
A way to remember it
FAINT
- F
- First-dose fall in blood pressure, with fainting
- A
- Abnormal ejaculation, most with tamsulosin
- I
- Intraoperative floppy iris syndrome in cataract surgery
- N
- Nasal stuffiness
- T
- Tiredness and weakness
Written for biofideX
Its name
-azosin means alpha-1 blocker (prazosin type)
Doxazosin and prazosin share it. Tamsulosin, an alpha-1 blocker used for an enlarged prostate, ends only in -osin; WHO lists it, with alfuzosin, as related.
- Every drug name stem
Its class
Alpha-1 blockers
Other alpha-1 blockers with a card:
Easily mixed up with central alpha-2 agonists, 5-alpha reductase inhibitors and beta blockers.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Blood pressure
Doxazosin is one of 27 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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