As the Mayo Clinic explains, kidney stones are formed when the concentration of certain dissolved substances in the urine gets too high. The kidneys work to remove waste products from the blood and regulate the electrolyte balance by filtering through the blood and concentrating the substances to be excreted into urine. Some chemicals (such as calcium, uric acid and struvite) can become too concentrated in the urine and form hard crystals called kidney stones. If these stones are small enough that they are excreted with the urine, they can become lodged in the urinary tract, leading to pain and discomfort.
Flomax and Kidney Stones
According to an article in the Chicago Tribune, one medication that can be used to treat kidney stones is tamsulosin. Tamsulosin is often used to treat the urinary symptoms of benign prostatic hyperplasia, a condition in which an enlarged prostate partially blocks the flow of urine from the bladder. This medication works to help relax the smooth muscle around the urinary tract, which allows for the easier passage of urine. Small kidney stones can be eliminated by excreting them along with the urine. Relaxing the smooth muscles in the urinary tract allows for the expansion of the urethra (which expels urine from the bladder), which makes it easier for kidney stones to be eliminated.
As the Merck Manual explains, tamsulosin works by interfering with the autonomic nervous system, which is involved in regulating smooth muscle tone. Tamsulosin binds to special proteins called alpha-1a adrenoceptors, which control signaling between the nervous system and the smooth muscle cells in the urinary system. When tamsulosin binds to these receptors, it blocks them, which keeps them from sending signals to tighten the smooth muscle. This causes the smooth muscle cells to relax, which in turns expands the diameter of the urethra.