Development of oral controlled-release tablet formulations based on diltiazem-carrageenan complex

Diltiazem HCl and lambda carrageenan react in distilled water to give a slightly soluble interaction product. The aim of this work was to verify the possible employment of lambda carrageenan-diltiazem (DTZ) complex in controlled-release formulations. The influence of complex particle size, compression force, pH of the dissolution medium, and tablet dimensions on drug release has been evaluated. The results confirm the suitability of the DTZ-carrageenan interaction product for controlled-release formulations. Good compaction properties allow tablets to slowly erode, with only the addition of the amount of hydroxypropyl methylcellulose (HPMC) necessary as a binding agent. The use of the finest sieve fraction results in the highest crushing strength values and in the slowest release rate, both in pH 1.2 and in pH 6.8. The force of compression does not affect the drug release for values over 16 kN. The release rate increases when the geometry of the tablet is varied so the surface/volume ratio of the tablet is increased, suggesting a release mechanism involving surface dissolution/erosion.