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.

• DoxazosinUnlike 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.
• PrazosinThe shortest-acting of the three alpha-1 blockers here. In the UK it is also licensed for heart failure that has not responded to diuretics or digoxin.
• TamsulosinThe prostate-selective member of the class: used for BPH, not for high blood pressure. It does not change PSA, and ejaculation problems and floppy iris syndrome are its best-known effects.

• Urinary symptoms of an enlarged prostate (BPH)
• High blood pressure (doxazosin, prazosin)
• Raynaud's phenomenon (prazosin)

• Fainting after the first dose (first-dose hypotension)Known forSerious
• Dizziness on standing (postural hypotension)Known for
• Floppy iris syndrome during cataract surgeryKnown for
• Headache
• Tiredness and weakness
• Drowsiness
• Stuffy or runny nose
• Ejaculation problems, most with tamsulosin
• Swollen ankles and legs (edema)
• Priapism: a painful erection that will not settleSerious

What the class has in common. Each drug's card has its own, and Known for marks what an exam expects you to know.

• Start low, with the first dose in the evening, and take care when another blood pressure drug is added.
• PDE5 inhibitors such as sildenafil add to the fall in blood pressure; the alpha blocker dose should be stable first.
• Tell the eye surgeon before cataract or glaucoma surgery: floppy iris syndrome can occur even after stopping.
• Rule out prostate cancer before treating urinary symptoms, as it often coexists with BPH.

Written for biofideX in plain words, after checking these references:

• Doxazosin tablets: label (DailyMed)
• Tamsulosin hydrochloride capsules: label (DailyMed)
• Prazosin hydrochloride capsules: label (DailyMed)
• Prazosin 0.5 mg tablets: SmPC (emc)
• Alpha-adrenergic antagonist (NCI Thesaurus)
• Doxazosin (NHS)
• Tamsulosin (NHS)

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.