Enthalpy relaxation studies of celecoxib amorphous mixtures.
OBJECTIVE
The purpose of this study was to compare the structural relaxation and molecular mobility of amorphous celecoxib (CEL) with that of CEL amorphous mixtures consisting of various excipients and to study the effect of different excipients on the relaxation of high-energy amorphous systems.


METHODS
The measurement of glass transition temperatures (Tg) and enthalpy relaxation were performed using differential scanning calorimetry. The interactions between drug and excipients and the absence of crystalline forms were further confirmed by conducting Fourier transform infrared spectroscopic and X-ray powder diffraction studies on same samples.


RESULTS
All samples exhibited a single Tg value. Polymers had a prominent effect on the lowering of the relaxation rate in amorphous CEL. The lowering of the rate of relaxation was directly dependent on the concentration and type of polymer used. The total enthalpy required for relaxation was same, although additives affected the rate of relaxation.


CONCLUSIONS
In absence of any specific interactions during Fourier transform infrared studies, it was concluded that the antiplasticizing activity of polymers is responsible for the stabilization of CEL amorphous systems. Glassy amorphous dispersions of CEL exhibited a complex type of relaxation pattern, which failed to fit in Kohlrausch-Williams-Watts equation with respect to calculation of relaxation time constants.
Kakumanu
Vasu Kumar
VK
Department of Pharmaceutical Technology (Formulations), National Institute of Pharmaceutical Education and Research (NIPER), Sector 67, Phase X, SAS Nagar, Punjab 160 062, India.
Bansal
Arvind K
AK
D002152:Calorimetry, Differential Scanning / Q000379:methods; D000068579:Celecoxib; D002626:Chemistry, Pharmaceutical; D011720:Pyrazoles; D013449:Sulfonamides / Q000138:chemical synthesis / Q000737:chemistry*; D013696:Temperature
D011720:Pyrazoles; D013449:Sulfonamides; D000068579:Celecoxib