Monitoring of dissolution induced changes in film coat composition by 1H NMR spectroscopy and SEM.

In our study we investigated the release mechanisms of coated oral dosage forms more deeply. The aim of the study was to monitor the buffer induced leaching out of water soluble compounds from Kollicoat SR films and to relate this process to the film properties and the release kinetics. Propranolol HCl tablets were coated with different amounts and ratios of polyvinyl acetate (Kollicoat SR) and poly(vinyl alcohol)-poly(ethylene glycol)-graft-copolymer (Kollicoat IR). Polyvinyl pyrrolidone (Kollidon 30) was added as a second water soluble polymer and triacetin as a plasticizer. In addition to kinetics of the drug release, the films were studied by SEM and 1H NMR spectroscopy. SEM micrographs revealed morphological changes of the tablet surface that were related to an alteration in film coat composition. The described 1H NMR method provided the opportunity to quantify the leaching of Kollicoat IR, Kollidon 30 and triacetin. Drug release kinetics were related to dissolution induced changes in coating composition. Permeability of the film coat increased, when about 90% of the water soluble polymers and plasticizer triacetin were leached out of the film coat.