Relationship Between Slugging Pressure and Brittle Fracture Tendency – A Case Study for Aspirin Tablets.

Objective – Slugging is a pre-compression technique for the dry granulation of hydrolysable drugs (e.g. aspirin). The study was carried out to relate the slugging load to the hardness of the granules and the brittle fracture tendency of the final (recompressed) tablets. Method – Varying compression load were applied to aspirin powder to form slugs, which were subsequently broken down to form granules. These were recompressed to give the final tablets. The hardness of the slugs was determined and taken as measure of the hardness of the resulting granules. The following tableting parameters were measured for the final tablets - tensile strength (T), packing fraction (Pf) and the brittle fracture index (BFI). Results - A high slugging load was associated with the formation of hard slugs and hence hard granules. Upon recompression the hardest granules formed the hardest tablets (T = 3.29MN m^-2) while the softest granules formed the softest tablets (T=1.09MN m^-2). In turn, the hardest tablets displayed the highest brittle fracture tendency (BFI = 0.59) compared with the softest tablets (BFI= 0.21). A positive linear correlation existed between tablet hardness (T) and BFI values (r = 0.98).Conclusion – The study showed that excessive slugging load produces hard aspirin granules which in turn yields hard but friable tablets.