Doxazosin
- Class: Alpha-1 blocker
- Used for: high blood pressure
- Say it: dox-AY-zoh-sin
- Forms: tablet
Doxazosin, terazosin and tamsulosin all end in -zosin and block alpha-1 receptors. Those receptors sit on vascular smooth muscle and on the prostate and bladder neck, so one drug loosens both.
The stem marks an alpha-1 blocker. Those receptors sit on vascular smooth muscle and on the prostate and bladder neck, so one drug loosens both. First dose at bedtime: removing the reflex that holds pressure up on standing is what causes the faint. All drug suffixes ›
Side effects
Common: dizziness, fatigue, ankle swelling
Serious: fainting after the first dose
Typical dose
1 mg at bedtime, titrated up to 8 mg
Double the dose no more often than every one to two weeks. The modified-release form starts at 4 mg and is gentler.
Check yourself
Why does doxazosin cause fainting after the first dose?
- Blocking alpha-1 removes the reflex vasoconstriction that holds pressure up on standing
- It slows the heart profoundly
- It causes sudden fluid loss through the kidney
- It triggers an allergic reaction in most patients
Show answer
A. Blocking alpha-1 removes the reflex vasoconstriction that holds pressure up on standing
Standing up normally triggers alpha-1-mediated constriction to stop blood pooling in the legs. With that reflex blocked, pressure drops as the patient rises — which is why the first dose goes in at bedtime.
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