Effect of excipients on the protection of compressed metronidazole pellets coated with methacrylic pellets coated with methacrylic acid copolymer

The effect of three different excipients (microcrystalline cellulose, lactose and dicalcium phosphate) was evaluated on the protection of coated (30 % of weight gain) metronidazole pellets during compression. Enteric-coated pellets manufactured with Eudragit(R) L 30 D-55 formed hard tablets; but the integrity of the coating was lost as determined by the in vitro dissolution. Sustained-release pellets manufactured with Eudragit(R) NE 30D, formed tablets with lower overall release after 24 h than the uncompressed pellets; the decrease was especially evident for the tablets compressed without filler-binder, however these tablets did not bind. A third group of pellets was manufactured having both enteric and sustained-release characteristics by coating with Eudragit NE 30D: Eudragit L 30 D-55 (15 % weight gain for each layer). The tablets from these pellets with dicalcium phosphate, as well as the uncompressed pellets, meet the USP XXV specifications for delayed release. Hardness of tablets depends, mainly, on the type of compressed pellets. Those prepared from uncoated and enteric-coated yielded the hardest tablets. Tablets from dicalcium phosphate showed the lowest hardness and the lowest in vitro drug release rates; therefore, it is hypothesized that the decreased release rate is related to the long disintegration time of the tablets.