Marbofloxacin.

IN THE TITLE COMPOUND, [SYSTEMATIC NAME: 9-fluoro-2,3-dihydro-3-methyl-10-(4-methyl-piperazin-1-yl)-7-oxo-7H-pyrido[1,2,3-ij][1,2,4]benzoxadiazine-6-carb-oxy-lic acid], C(17)H(19)FN(4)O(4), the carbonyl and carboxyl groups are coplanar with the quinoline ring, making a dihedral angle of 2.39 (2)°. The piperazine ring adopts a chair conformation and the oxadiazinane ring displays an envelope conformation with the CH(2) group at the flap displaced by 0.650 (2) Šfrom the plane through the other five atoms. The mol-ecular structure exhibits an S(6) ring motif, owing to an intra-molecular O-H⋯O hydrogen bond. In the crystal, weak C-H⋯F hydrogen bonds link mol-ecules into layers parallel to the ab plane.