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Tablets & Capsules May 2019 41 plastic-elastic materials. Another essential feature of calcium phos- phates is their low sensitivit y to lu b r ic a nt s . In c r e a s e d lu b r ic a nt amounts or longer mixing times do not significantly affect the compac- tion properties of powder mixtures containing calcium phosphates. Figures 2, 3, and 4 compare the tablet hardness (breaking force), porosity, and size (expressed as tab- let volume) of placebo tablets pro- duced using four DC calcium phos- phate products manufact ured by B u d e n h e i m ( D i - C a f o s D16 0 , Di-Cafos A150, Di-Cafos A60, and Tri-Cafos 50 0). The tablets con- tained 99.5 percent of the selected calcium phosphate and 0.5 percent lubr ic ant (ma g ne siu m stear ate). Powder mixtures were compressed into t ablet s u sing a F et te 102i rotar y tablet press at compaction forces of 10, 20, and 30 kN. As the results show, both anhy- drous and dihydrate calcium phos- phates have ver y good tableting properties and can produce hard tablets even at relatively low com- paction forces. It should be noted that, in the case of Di-Cafos A150, the compaction force has a very sig- nificant impact on tablet hardness. Figure 5 Effect of tribasic calcium phosphate (Tri-Cafos 500) admixture on tablet hardness Breaking force (N) Compression force (kN) 350 300 250 200 150 100 50 0 10 20 30 Di-Cafos A150 +10% Tri-Cafos 500 +20% Tri-Cafos 500 +30% Tri-Cafos 500 they exhibit very good compaction properties and result in hard tablets even at relatively low compression forces [5, 6]. Tribasic calcium phos- phate behaves differently, primarily undergoing plast ic defor mat ion during compression. Its high binding capacity results from the extensive specific surface area and the result- ing large number of potential bind- ing sites between particles [5, 7]. Tablets made with calcium phos- phates do not expand in volume upon ejection from the die in a tab- let press, which is a common phe- no me non w ith mor e ela s t ic or the same quantity of excipient. This is of significant importance when working with drug substances char- acterized by poor flowability and / or compactibility. The behavior of calcium phos- phate excipients in aqueous envi- r o n m e n t s i s v e r y i m p o r t a n t , because of its potential impact on a drug product's efficacy. Generally, calcium phosphates are insoluble in aqueous media at neutral or alkaline pH but are soluble in diluted acids, s uch as 0.1 mol / L hyd rochlor ic acid. T hat is why they dissolve completely in the acidic environ- ment pr evailing in the stomach without any risk of retaining the drug in the tablet matrix. Conse- quently, there is no perturbation in dissolution behavior and absorption from the gastrointestinal tract. Also, calcium phosphates do not swell or form hydrogels when they come into contact with water or aqueous solutions. They do not dis- integrate easily themselves, but by applying small amounts of com- monly used disintegrants, such as croscar mellose sodium or cross- linked polyvinylpyrrolidone, formu- lators can produce tablets with a very short disintegration time. Dibasic calcium phosphates are not hygroscopic and, under the condi- tions normally prevailing in a labora- tory or manufacturing area, are chem- ically and physically stable [1, 6]. Tablets containing these substances do not tend to undergo changes in tablet hardness if properly stored [8]. Anhydrous organic excipients tend to form hydrates when in con- tact with even small amounts of water vapor in the air, but this nega- tive effect does not occur with cal- cium phosphates. Anhydrous dibasic calcium phosphate does not form hydrates even if mixed with water for an extended period of time. Tableting properties of DC calcium phosphate excipients Dibasic calcium phosphates are hard, inorganic compounds that pri- mar ily undergo br it tle f ract u r e during compression. As a result, Tablets made with calcium phosphates do not expand in volume upon ejection from the die in a tablet press, which is a common phenomenon with more elastic or plastic-elastic materials.