Compression-Coated Tablet for Colon Targeting: Impact of Coating and Core Materials on Drug Release

Abstract

This work was envisaged to develop compression-coated tablets using a blend of Ca+2 ion cross-linked carboxymethyl xanthan gum (CMXG) and sodium alginate (SAL) for delayed release of immediate pulse release tablets of prednisolone (PDL) in the colon without the need of colonic bacterial intervention for degradation of the polysaccharide coat. The core tablets containing PDL and other compatible excipients were prepared by direct compression method and subsequently compression coated with different ratios of CMXG and SAL. Long Tlag, the time required to restrict the drug release below 10%, and short Trap, the time required for immediate release following the Tlag, were considered as suitable release parameters for evaluation of colon targeting of PDL tablets. Among the various compression coats, a blend of CMXG and SAL in a ratio of 1.5:3.5 provided Tlag of 5.12 ± 0.09 h and Trap of 6.50 ± 0.05 h. The increase in microcrystalline cellulose (MCC) and crospovidone (CP) in the core tablets did not change Tlag significantly although decreased the Trap marginally. Inclusion of an osmogen in the core tablets decreased the Tlag to 4.05 ± 0.08 h and Trap to 3.56 ± 0.06 h. The increase in coat weight to 225 mg provided a reasonably long Tlag (6.06 ± 0.09 h) and short Trap (4.36 ± 0.20 h). Drug release from most of the formulations followed the Hixson-Crowell equation and sigmoidal pattern as confirmed by the Weibull equation. In conclusion, tablets, compression coated with CMXG and SAL in a ratio of 1.5:3.5 and having 225-mg coat weight, were apparently found suitable for colon targeting.