Polymorphism in Piroxicam

Piroxciam is a polymorphic drug. However, reports on the number and nomenclature of the polymorphs of piroxicam and the complete hydrogen-bonding patterns of piroxicam molecules in the crystal forms are in conflict and are sources of confusion, which we attempt to clarify. The difference in energy of the two polymorphs, I and II, of piroxicam arises predominantly from the difference between their lattice energies, rather than between their conformational energies. The detailed hydrogen-bonding networks of the two polymorphs are described and compared. Despite stabilization of the polymorphs by hydrogen bonds, a loss of polymorphic memory was observed upon cryogrinding the two polymorphs, leading to differences in recrystallization behavior between amorphous piroxicam prepared from polymorphs I and II.