Health and Prostate

Generic Name Drug: Tamsulosin Hydrochloride
Trade Name Drug: Flomax (Boehringer Ingelheim Pharmaceuticals, Inc.)
Use: Treatment of signs and symptoms of benign prostatic hyperplasia

Benign prostatic hyperplasia (BPH) is a condition that results in proliferation of the stromal/epithelial cells of the prostate gland. This proliferation produces related symptoms such as dysuria, urinary retention, urinary obstruction, and urgency. The prevalence of BPH is age-dependent; approximately 66% of men older than age 65 show some symptoms.

Currently available treatment for the management of BPH includes alpha- antagonists, 5-alpha-reductase inhibitors, antiandrogens, and gonadotropin-releasing hormone analogs. Tamsulosin, which is an alpha-1A-adrenoreceptor antagonist, has been studied for use in the treatment of BPH.

How It Works

There is a large quantity of alpha-1 adrenoreceptors in the prostate, prostatic capsule, prostatic urethra, and bladder neck. Three subtypes of alpha receptors have been identified in the human prostate — alpha-1a, alpha-1b, and alpha-1d. Of these three, alpha- 1a is the predominant subtype. Tamsulosin (Flomax) is an alpha-1A-adrenoreceptor antagonist; it causes a blockade of the receptors, resulting in smooth muscle relaxation in the prostate and bladder neck. This relaxation, in turn, causes an improvement in the urinary flow rate and a reduction in the symptoms of BPH.

Flomax: Clinical Tips

An open-label extension study, as well as other trials, concluded that tamsulosin is safe and effective in the treatment of BPH. The only known associated side effects are abnormal ejaculation and dizziness. This extension study will continue for another 4 years to determine if the safety and efficacy profile can be maintained on a long-term basis.

Over 90% of tamsulosin (Flomax) is absorbed following oral administration of a 0.4-mg dose under fasting conditions. Tamsulosin is extensively bound to protein. Administration of tamsulosin with food causes a 30% decrease in bioavailability and increased time to maximal plasma concentration. Tamsulosin is extensively metabolized by the liver; only about 10% is excreted via the urine as unchanged drug.

Flomax (tamsulosin) has certain advantages over other alpha-antagonists that are used in the treatment of benign prostatic hyperplasia. Because of its specificity for alpha-1a receptors, it seems to leave alpha receptors in the blood vessels alone. Hence, it is associated with less orthostasis than are other alpha-antagonists. Also, there is no need to titrate tamsulosin to the recommended dose, as with other alpha-antagonists, which must be initiated at lower doses, then increased gradually to avoid first-dose syncope and orthostasis. Tamsulosin is widely used in Europe. If things go well, it may become the drug of choice in the treatment of BPH in the United States as well.