This compound can be obtained by a process which comprises reacting 4-amino-2-ethoxy-5-nitrobenzoic acid (I) with 4-amino-1-(3-cyclohexen-1-ylmethyl)piperidine (II) in the presence of triethylamine and ethyl chloroformate. The resulting free base (III) is salified with L-(+)-tartaric acid to give the corresponding salt.