5-Thia-1-azabicyclo(4.2.0)oct-2-ene-2-carboxylic acid, 7-(2-((2,3-dioxo-4-ethyl-1-piperazinyl)formamido)-3-hydroxybutyramido)-7-methoxy-3-(((1-methyl-1H-tetrazol-5-yl)thio)methyl)-8-oxo-, monosodium salt, (6R-(6-alpha,7-alpha,7(2R*,3S*)))-