(6r-(6-alpha,7-alpha))-7-((((2-amino-2-carboxyethyl)thio)acetyl)amino)-7-methoxy-3-(((1-methyl-1h-tetrazol-5-yl)thio)methyl)-8-oxo-5-thia-1-azabicyclo(4.2.0)oct-2-ene-2-carboxylic acid monosodium salt