CALCIUM PHOSPHATES IN PHARMACEUTICAL TABLETTING .1. PHYSICO-PHARMACEUTICAL PROPERTIES

Ten commercially available calcium phosphates used for direct tabletin g were evaluated. The particle size distributions, powder properties, sorption isotherms and pH values of aqueous slurries were compared. Al l samples showed good or at least sufficient flowability. Scanning ele ctron micrographs illustrated the different kinds of manufacturing and gave hints on their expectable behaviour under compaction pressure. T he sorption isotherms of identical chemical substances, which had been manufactured by different methods, differed strongly. This can be rel ated to their specific surface areas. Most of the hydroxylapatites hav e large surface areas and can absorb up to more than 15% water at 93% relative humidity. Dibasic calcium phosphate dihydrate was non-hygrosc opic and absorbed less than 1% water. With the exception of monobasic calcium phosphate monohydrate all calcium phosphates behaved quite neu tral in water. Monobasic calcium phosphate monohydrate can be regarded as a solid acid. Although the calcium phosphates are usually stable s ubstances, the role of crystal water in the case of dibasic calcium ph osphate dihydrate and monobasic calcium phosphate monohydrate is probl ematic due to possible interactions with active ingredients.