X-ray studies on piroxicam modifications

The anti-inflammatory drug piroxicam, 4-hydroxy-2-methyl-N-(2-pyridyl)2H-1,2- benzothiazine-3-carboxamide-1,1-dioxide, crystallizes in three different forms, two anhydrates and one monohydrate. Crystal structure analyses of the monohydrate and one of the anhydrate were carried out by Bordner et al. and Kojić-Prodić et al., respectively. In this paper the results of the analysis of the third piroxicam modification and of an independently performed structure determination of the monohydrate are reported. Molecular structures and hydrogen bonding of all modifications are discussed.