The influence of additives on the spreading coefficient and adhesion of a film coating formulation to a model tablet surface.

The surface energies of film coating formulations based on hydroxypropyl methylcellulose and containing microcrystalline cellulose, lactose and Tween 20, respectively, have been assessed. The approach taken allowed the components of the surface energy, in terms of the Lifshitz-van der Waals and the acid-base contributions, to be determined. Spreading coefficients of these coating formulations were determined on a model tablet surface whose surface energy had been similarly characterised. The determined spreading coefficients were high and positive indicating that spreading and wetting would not be a controlling factor in the formation of an adequate film coat. The adhesion of the coats to the core was measured and showed that the inclusion of additives influenced the adhesion of the film. Maximum adhesion was obtained when microcrystalline cellulose was included in the coating formulation that presumably allowed a strong interaction with the same component in the tablet core. Adhesion was enhanced when the tablet cores were made at a higher compaction force. Atomising air pressure had little influence on the adhesion.

An in vitro investigation into the potential for bimodal drug release from pectin/chitosan/HPMC-coated tablets.

The influence of disintegrant on the water uptake and subsequent disintegration force developed was investigated in a simple tablet formulation. The results indicated that a reasonable correlation existed between water uptake and disintegration force for the disintegrants screened with cross linked polyvinyl pyrrolidone (PVP XL) showing a proportionally higher disintegration force for the amount of water imbibed. Two tablet formulations, intended to promote accelerated drug release in the colon, were prepared, with and without PVP XL, and film coated with a mixture of pectin, chitosan and HPMC. The two systems showed different drug release rates which were influenced by the pH of the dissolution medium. In the presence of pectinolytic enzyme, drug release was faster when compared to release in buffer alone for both systems although the mechanism differed for each. Drug release in simulated gastrointestinal conditions showed a bimodal profile with the increased drug release rate being triggered by the action of pectinolytic enzymes.

Selective drug delivery to the colon using pectin:chitosan:hydroxypropyl methylcellulose film coated tablets.

A study has been carried out to assess the potential of pectin:chitosan:hydroxypropyl methylcellulose (HPMC) (P:C:H) films for colonic drug delivery. Radiolabelled (99mTc) tablets were coated with a 3:1:1, P:C:H film and administered to human volunteers. The gastro-intestinal transit of the tablets was assessed by gamma scintigraphy. The results showed that in all cases (n=4), the tablets were able to pass through the stomach and small intestine intact. Break up of the tablets commenced once they were in the colon, due to degradation of the coat by colonic bacteria. The study has highlighted the potential of this coating system for colonic drug delivery.

The potential use of mixed films of pectin, chitosan and HPMC for bimodal drug release.

Polyelectrolyte complex (PEC) formation between pectin USP and chitosan was investigated by examining the viscosities of supernatant solutions after removal of the precipitated complex. The amount of pectin, relative to chitosan, required for optimal PEC formation increased as the pH of the solution was reduced. At pH values of less than 1.3, there was no evidence for the formation of the PEC. Swelling studies conducted on pectin/chitosan films, showed minimal swelling occurring when the pectin:chitosan weight ratio was optimal for PEC formation, suggesting the formation of the PEC in situ. The permeability of the films to paracetamol as a model compound was dependent on film composition and was markedly increased after exposure to pectinolytic enzymes, used to mimic conditions in the colon. It may be implied from the results that similar formulations, applied as a film coat to tablets, could be used to achieve bimodal drug release with colonic conditions acting as a trigger for an increased rate of release.