In the title 1:1 co-crystal, C9H10N4O2S2·C6H9N3O2 [systematic name: 4-amino-N-(5-methyl-1,3,4-thiadiazol-2-yl)benzenesulfonamide–2-amino-4,6-dimethoxypyrimidine (1/1)], the sulfamethazole molecule is found in the form of the imidine tautomer. In the crystal, the components are linked by a pair of N—H...N hydrogen bonds, which generate an R22(8) loop. Further N—H...N and N—H...O hydrogen bonds link the dimers into [100] chains.
