Meloxicam hydro-chloride.

The title salt, CHNOS ·Cl [systematic name: 2-(4-hy-droxy-2-methyl-1,1-dioxo-1,2-benzo-thia-zine-3-amido)-5-methyl-1,3-thia-zol-3-ium chloride] is the hydro-chloride derivative of meloxicam, a drug used to treat pain and inflammation in rheumatic disorders and osteoarthritis. Although its mol-ecular structure is similar to that previously reported for the hydro-bromide analogue, both salts are not isomorphous. Different crystal structures originate from a conformational modification, arising from a degree of rotational freedom for the thia-zolium ring in the cations. By taking as a reference the conformation of meloxicam, the thia-zolium ring is twisted by 10.96 and -16.70° in the hydro-chloride and hydro-bromide salts, while the 1,2-benzo-thia-zine core is a rigid scaffold. This behaviour could explain why meloxicam is a polymorphous compound.