The effect of plasticizer type and concentration on the incidence of bridging of intagliations on film-coated tablets

Abstract

results were presented to show that bridging of the formed. This gel structure then contracts as f u r t b intagliations or monograms on a film coated tablet was solvent is lost until a viscoelastic film is formed. It is the a manifestation of the stress distribution within the film and occurred when the stresses inherent in the film due to shrinkage on the evaporation of solvent were very high. It was also shown that the incidence of this defect could be minimized by decreasing the thickness of the film. This study reports data on the effects of plasticizer and plasticizer concentration on the incidence of this same defect.The tablet substrate was the same as that used previously (Rowe & Forse 1980b). The tablets were coated with a film formulation consisting of a 5% w/v aqueous solution of hydroxypropyl methylcellulose (Pharmacoat 606Shinetsu Chemical Co., Japan) to which was added either glycerol, propylene glycol or polyethylene glycol 200 at varying concentrations (10. 20 and 30% w/w based on polymer). Film coating was carried out in a 24 inch Accelacota (Manesty Machines Limited) using an airborne spray system at an application rate of 50 in1 min-I and inlet air temperature of 60 "C. The same volume of coating solution was applied in each case to give a film thickness of 2G22pm. In order to assess the incidence of bridging, 1000 tablets were withdrawn at the end of the run, visually inspected and the number with any signs of defect counted and expressed as a percentage.The effect of plasticizer and plasticizer concentration on the incidence of bridging is shown in Fig. 1. It can be seen that at the 10 and 20% w/w level the rank order of plasticizer efficiency as measured by the lowering of the incidence of the defect is polyethylene glycol 200> propylene glycol > glycerol. At the 30% level the results for the polyethylene glycol 200 and propylene glycol are not significantly different.The concept of stresses being developed in a film coating by its shrinking over a tablet substrate on evaporation of the solvent was first proposed by Rowe (1978) to explain apparently anomalous filmltablet adhesion results. It has now been expanded to explain the causes of such film defects a s cracking, edge splitting and bridging (Porter 1980; Rowe & Forse 1980a.b). Before a discussion of how these stresses will be modified in the presence of plasticizers, it is pertinent to discuss how the stresses are developed during the formation of a polymer film from a solution of that polymer. Firstly, the solvent evaporates until, at a certain polymer concentration, a gel consisting of a Correspondence. dimensional constraint of a film contracting on r relatively immobile substrate that invariably causu stresses to develop. During this process, polymer chain mobility is an important factor in influencing the magnitude of the stresses developed. When the polyma chains are mobile, as in the case of the polymer solution and to a certain extent the gel, they will orientate themselves in such a way as to dissipate any stress@ formed. Ho...

Thermal Characterization of Drug/Polymer and Excipient/Polymer Interactions in Some Film Coating Formulation

“…The results obtained indicate the consequences of this phenomenon in film coating practice would be dependent on the nature and extent of interaction between the excipient/drug and film coating polymer. It is generally accepted that plasticization, which manifests as a fall in Tg, Ts and/or crystallinity (Moelter & Schweizer 1949;Okhamafe & York 1985a, b), often lowers the incidence of film coating defects such as cracking, edge splitting and bridging of intagliation (Rowe 1981(Rowe , 1982. This is usually desirable.…”

Influence of Process Parameters on Tablet Bed Microenvironmental Factors During Pan Coating

“…However, it was particularly interesting to note that the HPMC/triacetin system also did not show any logo bridging. This observation was not an obvious one, although there is limited existing literature that shows a relationship between plasticizer type (and concentration) and logo bridging observations (30); however, in that study, triacetin was not studied. It can be postulated that the HPMC/triacetin system offered better adhesion to Cross-section of a coated tablet showing that the underlying cause of logo bridging in this study was the film not adhering well to the tablet substrate the tablet substrate and/or reduced internal stresses within the film coat to mitigate the incidence of logo bridging.…”

Spatially resolved characteristics of pharmaceutical sprays

“…Not often explored are the roles that the spray and its characteristics play on film coat quality. Studies that do relate film coat quality to spray characteristics are: Kim et al1 and Rowe and Forse,2 who reported that incidences of logo infilling (bridging) increased as liquid supply rate increased. Twitchell,3 Twitchell et al,4 and Reiland and Eber,5 who found that increasing the atomizing air pressure or decreasing the gun‐to‐target distance resulted in a smoother film coat. Twitchell,3 who noted that a decrease in gun‐to‐target distance decreased film surface roughness. Ruotsalainen et al,6 who determined that film surface roughness increased with an increase in liquid supply rate. Fisher and Rowe7 and Rowe,8 who observed that film‐to‐tablet adhesion decreased as liquid viscosity increased. Twitchell3 and Rowe and Forse,9 who found that increasing the local spray mass flux at the tablet bed, achieved by increasing the liquid supply rate or changing the spray pattern from elliptical to circular, decreased the incidence of film splitting. …”