Behaviour and transit of tamsulosin Oral Controlled Absorption System in the gastrointestinal tract

To assess the in vivo behaviour, gastric emptying time and gastrointestinal transit of the new tablet formulation of tamsulosin which uses the Oral Controlled Absorption System (OCAS) technology and to relate gastrointestinal transit parameters to the profile of the plasma concentration time curve.

After breakfast, 8 healthy male subjects received a single tamsulosin OCAS 0.4 mg tablet labelled with 4MBq technetium-99m. Scintigraphic images were taken immediately after dosing, every 15 min until 15 h post-dose and at 24 h post-dose. Blood samples for pharmacokinetic analysis were taken up to 24 h after dosing. Safety was assessed by physical examinations, vital signs, laboratory safety evaluations and adverse events monitoring.

A mean C(max) of 7.84 +/- 2.54 ng/mL was achieved after 5.13 +/- 1.25 h (t(max)). The mean gastric emptying time for the tablet was 4.1 +/- 2.5 h. Mean transit time through the small intestine was 3.6 +/- 2.9 h; the mean colonic arrival time 7.7 +/- 2.9 h post-dose and the mean release time (spread of the technetium-99m label from the tablet core) 12.3 +/- 1.7 h post-dose. In all cases where release of the radiolabelled tablet was observed, this occurred within the colon. Variations in gastric residence, small intestinal transit or colonic residence did not apparently influence release time or site.

The results suggest that tamsulosin is released from the OCAS formulation throughout the entire gastrointestinal tract, including the colon, indicating consistent and continued 24-h drug release. This correlates with a more consistent pharmacokinetic profile.