Prostulax Mechanism of Action

Alpha-1-Adrenoceptor Antagonist.
Pharmacology: Mechanism of Action: Tamsulosin binds selectively and competitively to postsynaptic alpha 1-receptors, in particular to the subtype alpha 1A, which bring about relaxation of the smooth muscle of the prostate, whereby tension is reduced.
Pharmacodynamic Effects: Prostulax (Tamsulosin HCl) increases maximum urinary flow rate by reducing smooth muscle tension in prostate and urethra and thereby relieving obstruction. It also improves the complex of irritative and obstructive symptoms in which bladder instability and tension of the smooth muscles of the lower urinary tract play an important role. Alpha 1-blockers can reduce blood pressure by lowering peripheral resistance.
Pharmacokinetics: Absorption: Tamsulosin Hydrochloride is absorbed from the intestine and is almost completely bioavailable. Absorption of Tamsulosin Hydrochloride is reduced by a recent meal. Uniformity of absorption can be promoted by the patient always taking Tamsulosin Hydrochloride after the same meal each day. Tamsulosin shows linear kinetics. After single dose of Prostulax (Tamsulosin HCl) in the fed state, plasma levels of Tamsulosin peak at around 6 hours and in the steady state, which is reached by day 5 of multiple dosing. C_max in patients is about two third higher that reached after single dose. Although this was seen in elderly patients, the same finding would also be expected in young ones. There is a considerable inter-patient variation in plasma levels both after single and multiple dosing.
Distribution: In man, Tamsulosin is about 99% bound to plasma proteins and volume of distribution is small (about 0.21/kg).
Biotransformation: Tamsulosin and its metabolites have a low first pass effect, being metabolized slowly. Most Tamsulosin is present in plasma in the form of unchanged drug. It is metabolized in the liver. No dose adjustment is warranted in hepatic insufficiency. None of the metabolites are more active than the original compound.
Elimination: Tamsulosin and its metabolites are mainly excreted in the urine with about 9% of a dose being present in the form of unchanged drug. After as single dose of Prostulax (Tamsulosin HCl) in the fed state, and in the steady state in patients, elimination half-lives of about 10 and 13 hours respectively have been measured. The presence of renal impairment does not warrant lowering the dose.