The purpose of the present
work was to study the compatibility of metronidazole with different pharmaceutical
excipients (hydroxypropyl methylcellulose, poly(ethylene oxide), microcrystalline
cellulose, dicalcium phosphate dihydrate, and anhydrous dicalcium phosphate)
using differential scanning calorimetry and diffuse reflectance spectroscopy.
Dicalcium phosphate dihydrate was the only excipient that showed interaction
with metronidazole even before storage. Changes referring to a possible transition
to dihydrate form were observed in the thermal curves of anhydrous dicalcium
phosphate after four weeks of storage. Although dicalcium phosphate dihydrate
can be replaced by the anhydrous form in pharmaceutical formulations, the
observed transition might negatively influence the stability of dosage forms.