Alpha-1A selective antagonist
Alpha-1A selective adrenergic receptor antagonist
- Spares vascular α1B → relaxes prostate/bladder neck with little BP drop
- Improves BPH voiding; not a BP-lowering drug
- Abnormal ejaculation common (most with silodosin)
- Floppy iris syndrome at cataract surgery
- Silodosin ~160-fold α1A over α1B; tamsulosin binds α1A ≈ α1D, ~10–20-fold over α1B
- No dose titration; orthostatic hypotension uncommon but possible
- ➔ prefer over prazosin/doxazosin/terazosin when BP is low or falls are a concern
- Off-label: expulsion of distal ureteral stones
- Starting before cataract surgery not advised; tell the eye surgeon (stopping may not prevent floppy iris)
- Silodosin: avoid with strong CYP3A4 inhibitors or CrCl <30; retrograde ejaculation ~28%
Drugs with this mechanism (2)
- Silodosin — Highly uroselective alpha-1A blocker for BPH.
- Tamsulosin — Uroselective alpha-1A blocker for BPH; floppy iris in cataract surgery.
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