Sudden rise of crystal growth rate of nifedipine near T(g) without and with polyvinylpyrrolidone.

The crystal growth of nifedipine in the beta polymorph has been measured from T(g) + 50 to T(g) - 20 K, where T(g) = 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 T(g) 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 T(g). 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 T(g) + 50 K, but reduced the growth rate by 100-fold at T(g) + 9 K. These kinetic features are relevant to predicting the stability of amorphous drugs.