FLOMAX CR (tamsulosin hydrochloride) is an alpha₁ adrenoreceptor (AR) blocking agent used for the treatment of lower urinary tract symptoms (LUTS) associated with benign prostatic hyperplasia (BPH). It exhibits selectivity for both alpha_1A and alpha_1D receptors over the alpha_1B AR subtype. These three AR subtypes have a distinct distribution pattern in human tissue. Whereas approximately 70% of the alpha₁-receptors in human prostate are of the alpha_1A subtype, the human bladder contains predominantly the alpha_1D subtype while blood vessels express predominantly alpha_1B subtype.

Stimulation/antagonism of each of the receptor subtypes gives rise to a distinct pharmacological effect.

Lower Urinary Tract Symptoms (LUTS) suggestive of benign prostatic obstruction (BPO) formerly referred to as symptomatic benign prostatic hyperplasia (BPH) are very common in men >50 years old; the prevalence increases with age. The symptoms associated with LUTS/BPH are comprised of two underlying components: the static and dynamic. The static component is related to an increase in prostate size caused, in part, by a proliferation of smooth muscle cells in the prostatic stroma. However, the severity of BPH symptoms and the degree of urethral obstruction do not correlate well with the size of the prostate. he dynamic component is a function of an increase in smooth muscle tone in the prostate and bladder neck leading to constriction of the bladder outlet. Smooth muscle tone is mediated by the sympathetic nervous stimulation of alpha₁ adrenoreceptors, which are abundant in the prostate, prostatic capsule, prostatic urethra, and bladder neck. Blockade of these adrenoreceptors can cause smooth muscles in the bladder neck and prostate to relax, resulting in an improvement in urine flow rate and a reduction in symptoms of BPH.

It is further believed that blockade of alpha_1D subtypes in the human obstructed bladder may be responsible for reducing detrusor overactivity and subsequent relief of storage symptoms.

FLOMAX CR (tamsulosin hydrochloride) is not intended for use as an antihypertensive drug.

The FLOMAX CR (tamsulosin hydrochloride) tablet is a novel formulation based on the Oral-Controlled Absorption System (OCAS), a patented gel matrix controlled-release technology designed to provide a consistent slow release of tamsulosin which is maintained throughout the gastro-intestinal tract, resulting in an adequate exposure, with little fluctuation, over 24 hours.

The pharmacokinetics of tamsulosin from the OCAS have been evaluated in adult healthy volunteers with doses ranging from 0.4 mg to 1.6 mg