Pectin/HPMC dry powder coating formulations for colon specific targeting tablets of metronidazole

The objective of this study was to develop a dry powder coating technique applied to colon targeting tablets containing metronidazole (MET) by using a pan coater. The coating formulation consisted of a polymer mixture (pectin/HPMC) and plasticizer (dibutyl phthalate). Dissolution rate of MET was conducted at pH 1.2, 7.4 and 6.8 in the presence of pectinolytic enzyme. The lag time release of MET was simultaneously controlled by enzyme signal in colonic medium and coating level. There was a significant correlation between the coating level and lag time release when the ratio of pectin: HPMC was from 1:1 to 3:1. SEM indicated a homogenous coating layer when coated tablets were cured at 100 °C. The lag time phase of drug release was prolonged one more hour when curing time increased from 24 to 72 h at 60 °C. The in-vitro lag time of optimal formulation was 6.01 h. The X-ray imaging study showed the presence of coated tablets in ascending and descending colon after 6 and 8 h of tablet administration, respectively. The obtained dry powder coating technique had potential to prepare pulsatile release systems with long lag time release and without using organic solvent.

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