Piroxicam–excipient (chitosan or cellulose) mixtures after mechanical
activation were investigated using DSC. Crystallization of amorphous piroxicam
was detected near 80°C in the mixtures of the components activated separately.
If the components in the mixture are activated together, amorphous piroxicam
does not crystallize at heating.
Both excipients interact with
piroxicam, decreasing its melting point and enthalpy of melting. Mechanical
activation intensifies the interaction, decreasing the melting point by 8°C
and reducing the enthalpy of melting two times.
Both excipients
interact identically with piroxicam, affecting identically its melting parameters.
Nevertheless, the two excipients affect its solubility in water very differently.
Cellulose does not change the solubility, but chitosan increases it ten times.
The mechanism of piroxicam dissolution from the mixture with an excipient
is discussed.
Keywords cellulose - chitosan - drug-excipient interaction - DSC - melting - piroxicam - solubility