Studies on stress dispersion in tablets - III. Suppression of fracture of coated film by an excipient during the preparation of tablets containing coated particles

In the manufacture of tablets containing coated particles, the coated film is damaged by stress concentration, which occurs in the tablet during compr ession. In the present investigation, tablets consisting of one of various excipients and coated particles were produced. The ability of the excipient to disperse the stress generating in the tablet and thus to reduce damage to the coated film was examined; the physical properties of the excipients related to stress dispersal were also investigated. Tablets containing coat ed particles, prepared utilizing aspirin (ASA) as the core particle and Eud ragit L30D55 as the enteric coating agent, were produced with fourteen kind s of widely used excipients. The degree of coated film damage during compre ssion, that is, the degree of stress dispersibility caused by various excip ients, was evaluated by the release rate of ASA from the tablet as per our previous report [1, 2]. The ASA release rate in tablets consisting of rente d particles, produced at compression pressures achieving practical crushing strength with porous calcium silicate (Florite RE) as the excipient, was t he lowest among all excipients employed This finding demonstrated that the degree of coated film damage was the lowest, indicating that stress dispers ibility was high. In contrast, the tablet release rate was greatest with co rnstarch as die excipient. Consequently, coated film damage was highest. Th is finding indicated that stress dispersibility for cornstarch was low. A g ood correlation was seen between the plastic energy, percentage in the comp ression energy during tabletting and the decreasing percentage of volume. A dditionally, a correlation was established between the plastic energy perce ntage and the release rate. It was established that, the higher the plastic energy percentage of the excipient the lower the release rate of ASA from the tablet. That is, stress dispersibility is high. These results show that sri-ess generating in the tablet during compressor? is dispersed by the ad dition of an excipient characterized by a large plastic energy percentage i n compression energy. This type of excipient suppresses film fracture durin g tableting of the coated particles.