The effect of compression forces on the stability of dibasic calcium phosphate dihydrate tablets in the presence of glutamic acid hydrochloride monitored by isothermal calorimetry

Dibasic calcium phosphate dihydrate (DCPD) has been widely used as tablet diluent in both wet granulation and direct compression. Although DCPD is considered as a stable and inert diluent, it has been reported that certain acetic drugs and humidity/temperature conditions can evoke the loss of crystalline water. This study investigates the ability of isothermal calorimetry to detect any incompatibility reaction between glutamic acid hydrochloride (GAHCL), as an acidic model drug, and DCPD. The study identified an exothermic and endothermic reaction between GAHCL and DCPD which are influenced by compression forces. A correlation between the tablet relaxation energy and the magnitude of the solid state reaction between GAHCL and DCPD was established.