-2-aryl-propionamide compounds of formula: wherein Ar is selected from: a) an Ar a which is selected in the group consisting of 4-isobutylphenyl, 3-benzoyl-phenyl; b) a phenyl group 3-substituted by isopropyl, c) a 2-(phenylamino)-phenyl of formula (III c): wherein the substituents P1 and P2 indicate that the two phenyl groups bear, each independently, mono-or poly-substitutions with C 1 -C 4 -alkyl, C 1 -C 3 - alcoxy groups, chlorine, fluorine and/or trifluoromethyl. R is hydrogen; X is: - a linear C 1 -C 6 alkylene, optionally substituted at C1 by a - CO 2 R 4 wherein R 4 is H; - a linear C 1 -C 6 alkylene optionally substituted at C1 by a-CONHR 5 group wherein R5 is OH; - (CH 2) m -CO-NH-(CH 2) n - wherein m and n are each independently an integer from 2 to 3; - (CHR')-CONH- n wherein n is an integer from 2 to 3 and R' is a methyl, having absolute configuration RorS; - a phenyl or phenylmethylene group of formula: - or X, together with the N atom to which it is bound and the R1 group, forms an azocycloaliphatic ring, NR 1 R 2 R 3 group represents a trimethylammonium, triethylammonium,, N-cyclohexylmethyl-N, N-dimethylammonium, N-cyclopentylamino-N, N-dimethylammonium, N-methyl-1-piperidinium, N-ethyl-1-piperidinium, N-methyl-4-morpholinium,N-methyl-4-thiomorpholinium, N-benzyl-N,N-dimethylammonium, N-allyl-1-piperidinium, 4-oxo-N-methyl-piperidinium group or X together with the amine N to which it is bound and with the R1 group, forms a nitrogen containing 5-6 membered heterocyclic ring and the substituents R 2 and R 3 represent independently a methyl or cyclohexyl residue, Z - represents a pharmaceutically acceptable counterion of quaternary ammonium salts, or said compounds are - {3-[2-(3-benzoylphenyl)-propionylamino] propyl}-N-isopropyl-N,N-dimethylammonium iodide or -{3-[2-(4-isobutylphenyl)-propionylamino] propyl}-N-ethyl-N, N-dimethylammonium iodide. Ar is selected from: a) an Ar a which is selected in the group consisting of 4-isobutylphenyl, 3-benzoyl-phenyl; b) a phenyl group 3-substituted by isopropyl, c) a 2-(phenylamino)-phenyl of formula (III c): wherein the substituents P1 and P2 indicate that the two phenyl groups bear, each independently, mono-or poly-substitutions with C 1 -C 4 -alkyl, C 1 -C 3 - alcoxy groups, chlorine, fluorine and/or trifluoromethyl. a) an Ar a which is selected in the group consisting of 4-isobutylphenyl, 3-benzoyl-phenyl; b) a phenyl group 3-substituted by isopropyl, c) a 2-(phenylamino)-phenyl of formula (III c): R is hydrogen; X is: - a linear C 1 -C 6 alkylene, optionally substituted at C1 by a - CO 2 R 4 wherein R 4 is H; - a linear C 1 -C 6 alkylene optionally substituted at C1 by a-CONHR 5 group wherein R5 is OH; - (CH 2) m -CO-NH-(CH 2) n - wherein m and n are each independently an integer from 2 to 3; - (CHR')-CONH- n wherein n is an integer from 2 to 3 and R' is a methyl, having absolute configuration RorS; - a phenyl or phenylmethylene group of formula: - or X, together with the N atom to which it is bound and the R1 group, forms an azocycloaliphatic ring, - a linear C 1 -C 6 alkylene, optionally substituted at C1 by a - CO 2 R 4 wherein R 4 is H; - a linear C 1 -C 6 alkylene optionally substituted at C1 by a-CONHR 5 group wherein R5 is OH; - (CH 2) m -CO-NH-(CH 2) n - wherein m and n are each independently an integer from 2 to 3; - (CHR')-CONH- n wherein n is an integer from 2 to 3 and R' is a methyl, having absolute configuration RorS; - a phenyl or phenylmethylene group of formula: - or X, together with the N atom to which it is bound and the R1 group, forms an azocycloaliphatic ring, NR 1 R 2 R 3 group represents a trimethylammonium, triethylammonium,, N-cyclohexylmethyl-N, N-dimethylammonium, N-cyclopentylamino-N, N-dimethylammonium, N-methyl-1-piperidinium, N-ethyl-1-piperidinium, N-methyl-4-morpholinium,N-methyl-4-thiomorpholinium, N-benzyl-N,N-dimethylammonium, N-allyl-1-piperidinium, 4-oxo-N-methyl-piperidinium group or X together with the amine N to which it is bound and with the R1 group, forms a nitrogen containing 5-6 membered heterocyclic ring and the substituents R 2 and R 3 represent independently a methyl or cyclohexyl residue, Z - represents a pharmaceutically acceptable counterion of quaternary ammonium salts, or said compounds are - {3-[2-(3-benzoylphenyl)-propionylamino] propyl}-N-isopropyl-N,N-dimethylammonium iodide or -{3-[2-(4-isobutylphenyl)-propionylamino] propyl}-N-ethyl-N, N-dimethylammonium iodide.