application of fluoroqinolone derivatives of general formula is taught , in which r 1 is alkyl , fluoroethyl , cyclopropyl or difluorophenyl , r 2 , r 3 and r 4 are identical or different and represent hydrogen atoms or methyl radicals , x is n or a group ═ cr 6 in which r 6 is a hydrogen or fluorine atom , or alternatively r 6 with r 1 and the atoms to which they are attached forms a six - membered heterocycle substituted with a methyl radical and containing an oxygen atom , and r 5 is a hydrogen atom , or represents an amino radical if r 6 is a fluorine atom , as well as of their salts , for obtaining a medicinal product intended for the preventive and / or curative treatment of pneumocystosis . ## str1 ##