A NEW MULTIPARTICULATE DELAYED RELEASE SYSTEM .2. COATING FORMULATIONAND PROPERTIES OF FREE FILMS

The influence of membrane composition on dissolution characteristics w as determined for the osmotically controlled delayed release system de scribed previously (Schultz and Kleinebudde, J. Control. Release 47 (1 997) 181-189). In a first step the influence of plasticizer lipophilic ity on dissolution and swelling characteristics was determined. Furthe rmore the effect of varying amounts of TEC as plasticizer and microniz ed talc was investigated. The mechanical properties of dry and swollen film samples and plasticizer elution from free films during swelling were determined and compared to dissolution results. Increasing plasti cizer lipophilicity led to an increase in swelling time of the pellets . Drug release started after maximum swelling of the pellets. The diss olution rate was decreased by the use of more lipophilic plasticizers. The plasticizers leached from the free films according to their solub ilities. The mechanical properties of film samples changed immensely w ithin the first minute of exposure to the dissolution medium. The type of plasticizer employed had no effect on the mechanical properties of the wet films. The statistical evaluation of the mechanical propertie s of dry and wet films containing various amounts of plasticizer and t alc indicated a significant effect of plasticizer content. In addition the dissolution rate was influenced mainly by the plasticizer fractio n. An increasing amount of talc had no effect on the mechanical proper ties of swollen films but increased the lag time of drug dissolution f rom the coated formulation.