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40 May 2019 Tablets & Capsules make them ideal candidates for use in DC tableting processes. T hey exhibit excellent flowability due to their favorable par ticle size and s h a p e. F u r t h e r m o r e, t h e y c a n improve the flow pattern of poorly flowing powders, which makes it relatively easy for formulators to prepare tableting mixtures that do not require granulation. Many different types of calcium phosphates are available on the pharmaceutical market, including coarse DC grades as well as fine grades mainly used in granulation processes. This article outlines the most important characteristics of several DC grades of calcium phos- phate, ident if ies their t ablet ing properties, and discusses the differ- ent formulation challenges they can help overcome. T he investigated products are dibasic calcium phos- phate dihydrate, two types of diba- sic calcium phosphate anhydrous, and tribasic calcium phosphate. Functional properties of calcium phosphates Grains of dibasic calcium phos- phate excipients consist of aggre- gates of fine primar y particles of various shapes and sizes, as shown in the scanning electron microscope (SEM) images in Figure 1a, b, and c. While the grains are almost spheri- cal, the surface is uneven and well developed, which facilitates uniform blending with other ingredients. Tribasic calcium phosphate par- ticles, as shown in Figure 1d, have a large specific surface area, and their structure resembles a sponge. This allows fine particles of other ingre- dients, including A PIs, to easily adhere to the larger calcium phos- phate particles during blending and improves mixing efficiency. Calcium phosphates are charac- terized by ver y high volumet ric mass density which, in conjunction with their favorable particle shape, provides excellent flow properties. Their high density allows formula- tor s to inc r ease the a mou nt of excipient in a dosage form without increasing its size or to decrease the size of a dosage form while using Figure 2 Calcium phosphate tablet hardness (breaking force) Breaking force (N) 350 300 250 200 150 100 50 0 10 20 30 Compression force (kN) Di-Cafos A150 Di-Cafos D160 Di-Cafos A60 Tri-Cafos 500 Figure 3 Calcium phosphate tablet porosity Tri-Cafos 500 Di-Cafos A150 Di-Cafos A60 Di-Cafos D160 Porosity (%) 55 50 45 40 35 30 25 20 15 10 Compression force (kN) 10 20 30 Figure 4 Calcium phosphate tablet size (volume) for tablets of equal mass Tablet volume (mm 3 ) 180 170 160 150 140 130 120 110 100 Compression force (kN) 10 20 30 Tri-Cafos 500 Di-Cafos A150 Di-Cafos D160 Di-Cafos A60