Source: Health Products Regulatory Authority (ZA) Revision Year: 2021 Publisher: Ranbaxy Pharmaceuticals {Pty) Ltd, 14 Lautre Road, Stormill Ext 1, Roodepoort, 1724, South Africa
A 34 Other
Pharmacotherapeutic category: Adrenergic α1-receptors antagonist
ATC: G04CA02
The product is designed exclusively for the treatment of diseases of the prostate.
Tamsulosin binds selectively and competitively to post-synaptic α1-adrenoreceptors, in particularly to the subtype alpha1A and alpha1D with relaxation of smooth muscle in the bladder neck and prostate, resulting in an improvement in urine flow rate. Alpha1-blockers reduce blood pressure by lowering peripheral resistance.
Tamsulosin increases the maximum urine flow rate. It relieves obstruction by relaxing the smooth muscle in the prostate and urethra.
It also improves the storage symptoms in which bladder instability plays an important role. These effects on storage and voiding symptoms are maintained during long-term therapy. The need for surgery or catheterisation is significantly delayed.
Alpha1-blockers can reduce blood pressure by lowering peripheral resistance. Tamsulosin is not intended for use as an antihypertensive medicine.
Tamsulosin is absorbed from the intestine and is almost completely bioavailable. Absorption of tamsulosin is reduced by a recent meal. Uniformity of absorption can be improved by the patient always taking tamsulosin after the same meal.
After a single dose of tamsulosin taken after a meal, plasma levels of tamsulosin peaked at approximately 6 hours.
In the steady state, which is reached by day 5 of multiple dosing, Cmax in patients is about two thirds higher than that reached after a single dose. Although this was seen in elderly patients, the same finding would also be expected in younger patients. There is a considerable inter-patient variation in plasma levels, both after single and multiple dosing.
In man tamsulosin is about 99% bound to plasma proteins and volume of distribution is small (about 0, 21 L/kg).
Tamsulosin has a low first pass effect, being metabolised slowly. Most tamsulosin is present in plasma in the form of unchanged medicine. It is metabolised in the liver. In rats, hardly any induction of microsomal liver enzymes was seen to be caused by tamsulosin. In vitro results suggest that CYP3A4 and also CYP2D6 are involved in metabolism, with possible minor contributions to tamsulosin hydrochloride metabolism by other CYP isozymes. Inhibition of CYP3A4 and CYP2D6 medicine metabolising enzymes may lead to increased exposure to tamsulosin hydrochloride (see section 4.4).
None of the metabolites are more active than the parent compound.
Tamsulosin and its metabolites are mainly excreted in the urine with about 9% of a dose being present as an unchanged drug. The elimination half-life after a single dose is about 10 hours. The elimination half-life in steady state is about 13 hours. The lowering of the dose in renal impairment is not warranted.
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