Physical characterization of dibasic calcium phosphate dihydrate and anhydrate.
The dehydration of different commercial brands of
dibasic calcium phosphate dihydrate (DCPD; CaHPO4.2H2O)
was examined over a range of temperatures and water vapor pressures. To
determine the main factors affecting the physical stability of DCPD, the
baseline characterization of DCPD and dibasic calcium phosphate anhydrate (DCPA;
CaHPO4) was conducted by thermogravimetric analysis, differential
scanning calorimetry and X-ray diffractometry. The
surface area and the DCPA content (present as an impurity) depended on the
commercial source of DCPD. The
larger particles contained a higher concentration of DCPA and the anhydrate
exhibited a concentration-dependent acceleratory effect on the dehydration of
DCPD. Unlike DCPD, DCPA is physically stable and resisted
hydration even when dispersed in water for over 7 months in the temperature
range of 4-50 degrees C. In
dosage forms containing DCPD, there is a potential for phase transformation to
DCPA, while the reverse transition, that is, DCPA --> DCPD appears to be
extremely unlikely. Thus, the risk of physical transformation can be minimized by
using DCPA in formulations.