Tamsulosin Tablets

Mechanism

The symptoms associated with benign prostatic hyperplasia (BPH) are related to bladder outlet obstruction, which is comprised of two underlying components: static and dynamic. The static component is related to an increase in prostate size caused, in part, by a proliferation of smooth musclecells 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. The 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 adrenoceptors, which are abundant in the prostate, prostatic capsule, prostatic urethra, and bladder neck. Blockade of these adrenoceptors 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. Tamsulosin, an alpha1 adrenoceptor blocking agent, exhibits selectivity for alpha1 receptors in the human prostate. At least three discrete alpha1 adrenoceptor subtypes have been identified: alpha1A, alpha1B, and alpha1D; their distribution differs between human organs and tissue. Approximately 70% of the alpha1 receptors in the human prostate are of the alpha1A subtype.

Pharmacokinetics

• Absorption: Well absorbed orally; bioavailability ~100%.
• Distribution: Highly protein bound (94–99%).
• Metabolism: Extensively metabolized in the liver via CYP3A4 and CYP2D6.
• Elimination: Excreted in urine and feces.
• Half-life: Approximately 9–13 hours.

Side Effects

• Dizziness
• Headache
• Orthostatic hypotension
• Abnormal ejaculation
• Rare: syncope, allergic reactions

Contraindication

• Hypersensitivity to Tamsulosin or other alpha‑blockers
• History of orthostatic hypotension
• Severe hepatic impairment

Interaction

• CYP3A4 inhibitors (ketoconazole): Increase plasma levels of Tamsulosin.
• Other antihypertensives: Additive hypotensive effect.
• PDE‑5 inhibitors (sildenafil, tadalafil): Risk of severe hypotension.
• Warfarin: Monitor INR due to possible interaction.

Warning and Precautions

• Monitor blood pressure regularly during therapy.
• Advise patients to rise slowly from sitting or lying positions.
• Use cautiously in renal or hepatic impairment.
• Discontinue if severe dizziness or fainting occurs.