By condensation of 1-ethyl-6,7,8-trifluoro-1,4-dihydro-4-oxoquinoline-3-carboxilic acid (I) with 3-(ethylaminomethyl)pyrrolidone (II) by means of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in acetonitrile.