Pharmacological compositions containing a hydroxamic acid derivative selected from (2S)-2-((4-((4-((1S)-1,2-dihydroxyethyl)phenyl)ethynyl)benzoyl)(methyl)amino)-N-hydroxy-N,2-dimethylmalonamide, (2S)-2-((4-((4-((1R)-1,2-dihydroxyethyl)phenyl)ethynyl)benzoyl)(methyl)amino)-N-hydroxy-N,2-dimethylmalonamide, and (2S)-N-hydroxy-2-((4-((4-((1S)-1-hydroxy-2-methoxyethyl)phenyl)ethynyl)benzoyl)(methyl)amino)-N,2-dimethylmalonamide, or a salt of said derivatives, and an antibiotic substance are useful in the treatment of gram-negative bacterial infections.
