Enoxacin trihydrate.

The structure of the title compound, 1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(piperazin-4-ium-1-yl)-1,8-naphthyridine-3-carboxylate trihydrate, C(15)H(17)FN(4)O(3).3H(2)O, has a zwitterion of enoxacin and three water molecules in the asymmetric unit. The zwitterions form sheets lying parallel to each other and are hydrogen bonded in a head-to-tail manner. The crystal structure is stabilized by the involvement of O and H atoms from all the water molecules in strong hydrogen bonds. The naphthyridine ring system is essentially planar, with the carboxylate group lying out of this plane at an angle of 26.13 (6) degrees and the ethyl group oriented at approximately right angles to this plane. The piperazinium ring adopts a chair conformation.