Solubility of calcium gluceptate and the preparation of calcium gluceptate injection USP

Samples of calcium gluceptate obtained over a period of several years from various sources have been examined by GC to analyze the relative proportions of α:β epimers, by powder x-ray diffraction to determine whether the material is crystalline or amorphous, and by thermal analysis to determine the number of molecules of water of crystallization. Samples made after about 1980 were the calcium salt of the α epimer of glucoheptonic acid. With the exception of calcium gluceptate from Merck Frosst Canada, which is not available commercially, the α epimer material was a crystalline hydrate containing 3.5 molecules of water of crystallization per molecule of salt. It is sparingly soluble in water, and therefore cannot be used to prepare the USP injection, which contains 21-23% w/v calcium gluceptate. In contrast, samples of calcium gluceptate manufactured before about 1980 were a very soluble amorphous anhydrate. A method is given for preparing a stable solution of Calcium Gluceptate Injection USP from the sparingly soluble material currently available.