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Tamsulosin (rINN) (// or //) is used in the treatment of difficult urination, a common symptom of enlarged prostate. Tamsulosin, and other medications in the class called alpha blockers, work by relaxing bladder neck muscles and muscle fibers in the prostate itself and make it easier to urinate.
More specifically, tamsulosin is an α1aadrenergic receptor antagonist used in the symptomatic treatment of benign prostatic hyperplasia (BPH). Tamsulosin was developed by Yamanouchi Pharmaceuticals (now part of Astellas Pharma) and was first marketed in 1996 under the trade name Flomax, and also under the name Omnic.
When alpha 1 receptors in the bladder neck and the prostate are blocked, this causes a relaxation in smooth muscle and therefore less resistance to urinary flow. Due to this the pain associated with BPH can be reduced.
Selective action of tamsulosin in alpha 1A/D receptors is controversial and over three quarters of tamsulosin registered human studies are unpublished. 
Tamsulosin is primarily used for benign prostatic hyperplasia, but can also assist the passage of kidney stones by the same mechanism of smooth muscle relaxation via alpha antagonism. Tamsulosin is also used as adjunct treatment of acute urinary retention. Multiple studies have shown patients will void more successfully after catheter removal if they are taking tamsulosin vs. placebo. Patients taking tamsulosin are also less likely to need re-catheterization.
- Immunologic: It contains a sulfa moiety, thus causing typical reactions to sulfa drugs.
- Ophthalmologic: Patients taking tamsulosin are prone to a complication known as floppy iris syndrome during cataract surgery. Adverse outcomes of the surgery are greatly reduced by the surgeon's prior knowledge of the patient's history with this drug, and thus having the option of alternative techniques.
- Severe hypotension. 
Tamsulosin has also affected sexual function in men. It can cause males to experience retrograde ejaculation. In males, retrograde ejaculation occurs when the fluid to be ejaculated, which would normally exit the body via the urethra, is redirected to the urinary bladder. Normally, the bladder sphincter contracts and the ejaculate goes to the urethra, the area of least pressure. In retrograde ejaculation, this sphincter does not function properly.
Use in combination therapy
The results of the CombAT (Combination of Avodart and Tamsulosin under the brand name Duodart) trial in 2008 demonstrated that treatment with the combination of dutasteride (Avodart) and tamsulosin provides greater symptom benefits compared to monotherapy with either agent alone for treatment of benign prostatic hyperplasia.  The CombAT trial became the medication Jalyn. It was approved by the FDA on June 14, 2010. This combination can be useful as it can take up to six months for any symptomatic relief to be found by 5-alpha-reductase inhibitors such as dutasteride compared to alpha-1 receptor blockers which can provide relief in some cases within 48 hours.
Tamsulosin was first marketed in 1996 under the trade name Flomax. It is now marketed by various companies under licence, including Boehringer-Ingelheim and CSL. Tamsulosin hydrochloride extended-release capsules are marketed under the trade names Urisurge(India), Flomax, Flomaxtra, Contiflo XL, Urimax and Pradif, although generic, non-modified-release capsules are still approved and marketed in many countries (such as Canada). In Mexico, it is marketed as Secotex and as Harnal D in Japan and Indonesia. In Egypt, Italy and Iceland, it is marketed under the trade name Omnic by Astellas Pharma Europe. The largest manufacturer of tamsulosin, drug substance, is Synthon.
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- http://www.bmj.com/content/347/bmj.f6320/rr/698284. Missing or empty
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- Jeong IG, You D, Yoon JH, et al. (February 2014). "Impact of tamsulosin on urinary retention following early catheter removal after robot-assisted laparoscopic radical prostatectomy: A prospective randomized controlled trial". Int. J. Urol. 21 (2): 164–8. doi:10.1111/iju.12225. PMID 23906190.
- PharmacistAnswers Tamsulosin & Catheterization Retrieved February 12, 2014.
- Medscape, Good Cataract Surgery Outcomes Possible in Intraoperative Floppy Iris Syndrome Due to Tamsulosin.
- Bird, ST; Delaney, JA; Brophy, JM; Etminan, M; Skeldon, SC; Hartzema, AG (2013 Nov 5). "Tamsulosin treatment for benign prostatic hyperplasia and risk of severe hypotension in men aged 40-85 years in the United States: risk window analyses using between and within patient methodology.". BMJ (Clinical research ed.) 347: f6320. PMID 24192967.
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- "Tamsulosin Side Effects". Drugs.com. Retrieved 2011-04-27
- Roehrborn CG, Siami P, Barkin J, et al. (February 2008). "The effects of dutasteride, tamsulosin and combination therapy on lower urinary tract symptoms in men with benign prostatic hyperplasia and prostatic enlargement: 2-year results from the CombAT study". J. Urol. 179 (2): 616–21; discussion 621. doi:10.1016/j.juro.2007.09.084. PMID 18082216.
- Australian Medicines Handbook
- Dr. Sandro Magnanelli; Dr.ssa Ada Maria Vetere. "Pradif 0,4 Mg Capsule Rigide A Rilascio Prolungato". Torrinomedica.it. Retrieved 15 November 2012.
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- "Novartis hits Astellas with transplant drug generic". Reuters. 11 August 2009. Retrieved 11 August 2009.
- Tamsulosin – information from USP DI Advice for the Patient
- Flomax (drugs.com) – U.S. product information
- Product label U.S. Food and Drug Administration (FDA)
- Flomax (Official Site)[dead link] – Official Site