Abstract: (1R,5S,6S)-6-[(R)-1-hydroxyethyl]-1-methyl-2-[(1,2-diiminomethyl)-4-pyrazol idinyl-thio-carbapenem-3-carboxylic acid is provided as an intermediate, which is converted into (1R,5S,6S)-2-[(6,7-dihydro-5H-pyrazolo[1,2-a][1,2,4]triazolium-6-yl]thio-6 -[R-1-hydroxyethyl]-1-methyl-carbapenem-3-carboxylate. This compound is an antibacterial agent, which also may be in the form of the corresponding acid or pharmaceutically acceptable salt, in which case there is included an anionic group balancing the traizolinium positive charge. As such as anionic group may be mentioned, for example, the chloride, acatate or carbonate. As the salt may be mentioned the alkali metal salts, for example, sodium.