Sustained delivery of captopril from floating matrix tablets.

The development of a controlled release formulation of captopril has been a challenge for some time. In this work, the in vitro sustained release of captopril from Metolose SH 4000 SR/sodium bicarbonate floating tablets has been studied, varying the proportions of Metolose and bicarbonate. This was studied at two different compaction pressures. Other studied variables include the kinetics of the hydration volume, the matrices floating time and the matrix density. The results show that matrices compacted at 55 MPa float in the dissolution medium for more than 8h while those compacted at 165 MPa float only when sodium bicarbonate is included in the formulation. The increase of the matrix polymer proportion increases the maximal hydration volume as well as the time to attain this maximum. The matrices hydration volume increases with the inclusion of sodium bicarbonate in the formulation. The matrix density is lower when compacted at 55 MPa. The drug release constant (k) decreases and the exponent indicative of the release mechanism (n) increases with increasing polymer contents. The drug released with time is lesser when sodium bicarbonate is included in the formulation. Carbon dioxide bubbles obstruct the diffusion path and decrease the matrix coherence. The effect of compaction pressure to reduce the drug release rate has to be made clear in further studies.