CRYSTAL FORM OF ANHYDROUS 7-([1 ALPHA,5 ALPHA,6 ALPHA]-6-AMINO- -3-AZABICYCLO[3.1.0]HEX-3-YL)-6-FLUORO-1-(2,4-DIFLUOROPHENYL)- -1,4-DIHYDRO-4-OXO-1,8-NAPHTHYRIDINE-3-CARBOXYLIC ACID, METHANESULFONIC ACID SALT, A METHOD OF ITS PREPARATION, PHARMACEUTICAL AGENTS BASED THEREON, AND THE USE OF THIS FORM

New crystal form, (I'), of 7-([1~a, 5~a, 6~a]-6-amino-3-azabicyclo [3.1.0] hex-3-yl)-6- fluoro-1-(2,4-difluorophenyl)- 1,4-dihydro-4-oxo-1,8- naphthyridine-3-carboxylic acid, methanesulphonic acid salt (I), is characterised by the following major peaks in its X-ray powder diffraction pattern: Peak number; 2~h( deg )Cu; d space: (1; 4.5; 19.5); (2; 7.7; 11.5); (3; 9.1; 9.7); (4; 13.6; 6.5); (5; 15.0; 5.9); (6; 18.2; 4.9); (7; 18.6; 4.8); (8; 22.8; 3.9). Disclosed is a crystalline form of anhydrous 7-([1.alpha., 5.alpha.,6.alpha.]-6-amino-3-azabicyclo[3.1.0]hex-3-yl)-6- -fluoro-1-(2,4-difluorophenyl)-1,4-dihydro-4-oxo-1,8- -naphthyridine-3-carboxylic acid, methanesulfonic acid salt which is characterised by the following major peaks in its X-ray powder diffraction pattern: peak no. 1: 2 theta (°C) Cu 4.5, d space 19.5; peak no. 2: 2 theta (°C) Cu 7.7, d space 11.5; peak no. 3: 2 theta (°C) Cu 9.1, d space 9.7; peak no. 4: 2 theta (°C) Cu 13.6, d space 6.5; peak no. 5: 2 theta (°C) Cu 15.0, d space 5.9; peak no. 6: 2 theta (°C) Cu 18.2, d space 4.9; peak no. 7: 2 theta (°C) Cu 18.6, d space 4.8; peak no. 8: 2 theta (°C) Cu 22.8, d space 3.9, has an advantageous stability for the formulation as an antibacterial agent. This form is prepared from a respective salt which do not exhibit the abovementioned properties, or from its monohydrate by heating in the presence of alcohol or a mixture thereof with an aprotic co-solvent. Pharmaceutical agents based upon the said salt and the use thereof for the treatment of bacterial infections.