tamsulosin
Meaning of tamsulosin: Relief arrives in days rather than months, because the drug changes muscle tone instead of shrinking the gland causing the obstruction.
Definition of tamsulosin
Tamsulosin is a medication that eases the urinary symptoms of an enlarged prostate by relaxing smooth muscle in the prostate and the neck of the bladder. It belongs to the alpha blocker class, which acts on the receptors that hold that muscle partly contracted. Relaxing the muscle widens the channel urine passes through, so flow improves without the gland changing size.
How does relaxing muscle improve urine flow?
The prostate wraps around the top of the urethra, the tube that carries urine out of the bladder. Two separate things narrow that tube as the gland enlarges. One is bulk, the extra tissue pressing inward. The other is muscle tone, since smooth muscle in the gland and in the bladder neck is held partly contracted by alpha-1 receptors. Tamsulosin blocks those receptors, the muscle relaxes, and the channel opens. The symptoms that ease are the obstructive ones: a weak or interrupted stream, hesitancy at the start, straining, and the sense that the bladder has not emptied. Muscle tone can change within a day or two, so the effect appears early rather than after months of treatment.
How is it different from a drug that shrinks the prostate?
| Alpha blocker, such as tamsulosin | 5-alpha-reductase inhibitor | |
|---|---|---|
| What it changes | Muscle tone in the gland and bladder neck | The size of the gland itself |
| How soon it acts | Days | Months |
| Effect on gland volume | None | Gradual reduction |
| Effect on a PSA result | None | Lowers it, which laboratories and clinicians account for |
The two classes are sometimes combined, one acting quickly on tone and the other slowly on bulk. Tamsulosin addresses the symptoms of benign prostatic hyperplasia only. It does not slow the growth of the gland, and it has no effect on prostate cancer.
Why is it described as selective?
Alpha-1 receptors are not confined to the prostate. They also help hold the walls of blood vessels partly contracted, which is why older, non-selective alpha blockers lowered blood pressure and could cause lightheadedness on standing. Tamsulosin binds more tightly to the receptor subtype concentrated in the prostate and bladder neck, so its effect on blood pressure is smaller, though not absent. One other site matters: the muscle that widens the pupil carries the same receptors, and the iris can behave unpredictably during cataract surgery in someone who has taken an alpha blocker, which is why eye surgeons ask about this class of medication beforehand.
Also known as
Used in a sentence
Tamsulosin was prescribed to help relieve urinary symptoms associated with the patient's enlarged prostate.
Good to know
Tamsulosin eases urinary symptoms by relaxing muscle tone rather than by shrinking the prostate, a mechanism distinct from the medications that reduce prostate size gradually over months.