Grinding of drugs with pharmaceutical excipients at cryogenic temperatures

The effect of cryogenic grinding on the piroxicam and its mixtures with polyvinylpyrrolidone (PVP) was studied by powder X-ray diffraction and differential scanning calorimetry (DSC). The crystallization of the amorphous piroxicam obtained during cryogrinding showed two events in a DSC curve (noticeable for pure piroxicam, and much more pronounced for the PVP-piroxicam mixtures). For the same measurement conditions, the intensity ratio of the peaks corresponding to the two events differed for the PVP-piroxicam mixtures of different drug-excipient ratios. The temperatures, at which these events were observed, increased with the increase in the PVP-concentration in the mixture. For the mixtures with a high relative content of PVP (>= 60%), crystallization was not observed at all. Only one glass transition was revealed for the mixture containing 80% PVP suggesting that a molecular alloy was formed.