Compressibility of gastroretentive pellets coated with Eudragit NE using a single-stroke and a rotary tablet press

In this study, 15 kinds of powders with different compression mechanisms were used in the process of filling-binding substances in tablets with pellets. Applied substances possessed dominant brittle time-independent mechanism or time-dependent viscoplastic, viscoelastic mechanism of compression. Using 6 kN compression force in a single-stroke tablet press during 150 ms of compression, damage to the polymer film and pellet core was found in all formulations. As a result, the authors observed an increase of releasing rate of verapamil hydrochloride (VH). A larger contact area between powders and pellets and connected with this better protective properties were ensured by powders with time-independent compression mechanism (eg, D-sorbitol or D-mannitol). Unsymmetrically applied compression force was a reason for inconsistent densification and insufficient protection of the pellets. Taking into consideration the low rotation speed of the turret (10 rpm) in the rotary tablet press, the total compaction time was much longer than in the single-stroke tablet press. The compression time in the case of the rotary tablet press should be considered as the sum of the precompression (about 130 ms) and main compression (about 280 ms) phase times. Compression force applied by upper and lower punch in the precompression and main compression phase was affected uniformly on the pellets' surface, and when protected against fragmentation, allowed only some slight deformation. The powders in tablet formulation were fragmentized and rearranged independent of their compression mechanisms. It was found that the releasing rate of VH from pellets compressed by rotary tablet press with 6, 12, and 18 kN of compression force was similar to the releasing rate from uncompressed pellets.