Biphasic drug release from film-coated tablets

A study was carried out into the biphasic drug release properties of film-coated paracetamol tablets. The tablet cores were formulated without a disintegrant and film-coated with a coating formulation consisting of pectin, chitosan and hydroxypropylmethylcellulose in a ratio of 6:1:0.37. The tablet cores and the film-coated tablets with coat weight gains (CWGs) of 6, 9 and 13% were evaluated for their water absorption (swelling) and drug release properties. All the tablets absorbed water from pH 6.0 Sorensen's phosphate buffer and the amount of water absorbed increased with an increase in tablet CWG. The addition of 100 microl/50 ml pectinolytic enzymes to the medium resulted in at least a 40% reduction in the amount of water absorption by the tablets, as compared to the medium without enzymes. When the enzyme concentration was increased to 200 microl/50 ml, there was a further reduction ( approximately 8% w/w) in the amount of water absorbed by the tablets. Drug release was controlled in upper gastrointestinal fluids and decreased with an increase in tablet CWG. Drug release was, however, accelerated in the presence of pectinolytic enzymes, consistent with the entry of the tablets in the colon. An evaluation of the drug release data by the Korsmeyer-Peppas equation showed the involvement of molecular diffusion and other factors such as film/tablet erosion and drug dissolution in drug release.