Sudden Rise of Crystal Growth Rate of Nifedipine near Tg without and with Polyvinylpyrrolidone

ABSTRACTThe crystal growth of nifedipine in the β polymorph has been measured from Tg + 50 to Tg − 20 K, where Tg = 315 K is the glass transition temperature. A sudden 10-fold rise of growth rate was observed as the temperature decreased from above to below Tg accompanied by a change of growth morphology. This is the same phenomenon reported by Oguni and coworkers [Hikima T, Adachi Y, Hanaya M, Oguni M. 1995. Phys Rev B 52:3900–3908] for other compounds of lower Tg. The phenomenon persisted in the presence of 1% polyvinylpyrrolidone (PVP). The presence of 1% or 2% PVP had little effect on the growth rate near Tg + 50 K, but reduced the growth rate by 100-fold at Tg + 9 K. These kinetic features are relevant to predicting the stability of amorphous drugs.