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 Ranbaxy 0.4 mg Prolonged release capsules after the same meal.
Tamsulosin shows linear kinetics.
After a single dose of tamsulosin 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, Cmax in patients is about two thirds higher than that reached after a single dose.
Although this was seen in the older 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. The volume of distribution is small (about 0.2 l/kg).
Biotransformation
Tamsulosin has a low first pass effect, being metabolised slowly. Most tamsulosin is present in plasma in the form of unchanged active substance. It is metabolized 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 drug metabolizing enzymes may lead to increased exposure to tamsulosin hydrochloride (see section 4.4 and 4.5).
None of the metabolites are more active than the original compound.
No dose adjustment is warranted in patients with mild to moderate hepatic insufficiency (see section 4.3).
Elimination
Tamsulosin and its metabolites are mainly excreted in the urine with about 9% of a dose being present in the form of unchanged active substance.
After a single dose of tamsulosin in the fed state, and in the steady state in patients, elimination half-lives of about 10 and 13 hours, respectively, have been measured.
No dose adjustment is necessary in patients with renal impairment.