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Excipients & Actives for Pharma No. 26, 2011 To investigate the influence of the type of filler, tablets with varying ratios of crospovidone grades and dicalcium phosphate anhydrate as filler were compressed (Figure 3). Again, the resulting tensile strength of the tablets depended on the grade and amount of the crospovidone used. The tablets containing Kollidon ® CL did not show an increase in tensile strength, whereas those containing Kollidon CL-F and Kollidon CL-SF showed increasing values. The increase was more pronounced for tablets made with dicalcium phosphate anhydrate compared to those containing lactose. Tensile strength [N/mm 2 ] 6 5 4 3 2 1 Lactose / Kollidon CL-SF Lactose / Kollidon CL-F Lactose / Kollidon CL In addition to good binder properties, tabletting excipients for direct compression should exhibit good flowability. All formulations were analyzed with a ring shear tester; the detected flow behavior is depicted in Figure 4, where different regions represent bulk flowability from very cohesive to free-flowing. Each tabletting mixture exhibited at least easy-flowing behavior. By adding different grades and ratios of crospovidone to lactose, flowability changed from free-flowing to easy-flowing. Kollidon CL-SF, which has the smallest particle size, led to formulations with the worst flowability. However, all analyzed tabletting mixtures still exhibited easy-flowing or free-flowing behavior. Adding Kollidon CL-SF produces a minor effect only on flow properties; this can be neglected during compression. For every batch, all analyzed tablets disintegrated disintegrated in less than 70 seconds. 0 FIGURE 1 Tensile strength of lactose/crospovidone tablets compressed at 255 MPa. (n = 10, mean ± s) Cumulative fraction [%] 0 20 40 60 80 100 100 80 60 40 Kollidon CL Kollidon CL-F Kollidon CL-SF Disintegrant [%] 20 0 1 10 100 1000 Particle size [µm] FIGURE 2 Particle size distributions of Kollidon CL, CL-F and CL-SF, measured with laser light diffraction. (n = 3) Page 6
Excipients & Actives for Pharma No. 26, 2011 Tensile strength [N/mm 2 ] 6 5 4 3 2 1 Lactose / Kollidon CL Lactose / Kollidon CL-F Lactose / Kollidon CL-SF Dicalcium phosphate anh. / Kollidon CL Dicalcium phosphate anh. / Kollidon CL-F Dicalcium phosphate anh. / Kollidon CL-SF Conclusion Crospovidone grades of small particle size can be used as combined disintegrants and binders. The tensile strength of the directly compressed tablets was almost tripled, depending on particle size and amount of crospovidone used. In addition to the dry binder properties, all mixtures containing different grades and ratios of crospovidone exhibited at least easy-flowing behavior. The combination of dry binder properties and easy-flowing behavior makes crospovidone an ideal excipient for direct compression. REFERENCES 0 0 20 40 60 80 100 Disintegrant [%] [1] Fell, J.T., Newton, J.M., (1970)."Determination of tablet strength by the diametral-compression test", Journal of Pharmaceutical Sciences 59 (5): 688-691. FIGURE 3 Tensile strength of lactose/crospovidone and dicalcium phosphate anh./crospovidone tablets compressed at 153 MPa. (n = 10; mean ± s) [2] McKenna, A. (1982). “Effect of particle size on the compaction mechanism and tensile strength of tablets.” Journal of Pharmacy and Pharmacology 34(6): 347-351. 3000 Very cohesive ff c =2 Cohesive Unconfined yield strength [Pa] 2000 1000 ff c =4 Easy-flowing ff c =10 Free-flowing 0 5000 7500 10000 Consolidation stress [Pa] FIGURE 4 Flowability of tabletting mixtures with different ratio of disintegrant. (blue symbols = Kollidon® CL-SF, red symbols = Kollidon® CL-F, green symbols = Kollidon® CL, black symbols = pure lactose) Page 7
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