ABSTRACT:
Press-coated tablets are able to release the core drug after of lag time and have potential for colon targeted drug delivery based on gastrointestinal transit time concept. This study investigated the factors influencing in vitro release characteristics of model drug prednisolone from press coated tablets. Prednisolone is a poorly water soluble drug having pH-independent solubility. Solubility enhancement of prednisolone with hydroxypropyl ß-cyclodextrin (HP ß-CD) was studied by phase solubility analysis. HP ß-CD increased solubility of prednisolone. Phase solubility studies suggested that 1:2 complex of prednisolone-HP ß-CD was formed. A physical mixture of prednisolone and HP ß-CD was incorporated in core tablet. The core tablet, prepared by a direct compression method, was designed to disintegrate and release drug quickly. To prepare press coated tablets, 50 % of coating polymer was first, followed by centering the core tablet and compressing with remaining 50 % of the coating polymer. Effect of Natrosol viscosity grades (Natrosol L, M and HHX), weight of Natrosol coating, different weight ratios of Natrosol-HHX: Natrosol M and different weight ratios of Natrosol-L: Natrosol M on the lag time of drug release was studied. The lag phase was markedly dependent on the weight ratios of Natrosol-HHX: Natrosol M or Natrosol-L: Natrosol M in coat. Larger coating weight of Natrosol M produced larger coating thickness around core tablet, which resulted in increased lag time and decreased drug release. Different lag times of the press-coated tablets from 2 to 9.5 hours could be modulated by changing the type and amount of Natrosol. Natrosol of higher viscosity (Natrosol HHX) provide better protection of the drug containing core, showing increased lag time and slower drug release. Incorporating low viscosity polymer (Natrosol-L) in coat leads to decrease in lag time and rapid drug release. The results indicate that Natrosol M coated tablet formulation is more suitable for transit (5.5 hrs) through stomach and small intestine and faster release of drug in colon.