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The pharmaceutical 2:1 co-crystal of meloxicam [MXM; systematic name: 4-hydroxy-2-methyl-N-(5-methylthiazol-2-yl)-2H-1,2-benzothiazine-3-carboxamide 1,1-dioxide] with acetylenedicarboxylic acid (ACA; systematic name: but-2-ynedioic acid), crystallizes with one MXM molecule and half an ACA molecule in the asymmetric unit, C14H13N3O4S2⋅0.5C4H2O4. The mid-point of the triple bond of ACA is located on an inversion centre. In the crystal, the two stereoisomers of MXM with respect to the N atom of the sulfonamide group are related by the inversion centre. The carbonyl and hydroxy groups belonging to the MXM molecule are involved in an intramolecular O--H⋯O hydrogen bond. The structure-forming motif includes two MXM molecules linked via an ACA conformer through N--H⋯O and O--H⋯N hydrogen bonds, similar to MXM co-crystals with other dicarboxylic acids. [ABSTRACT FROM AUTHOR]