(4R,5S,6S)-3-[[3S,5S)-5-[(DIMETHYLAMINO)CARBONYL]-3-PYRROLIDINYL]THIO]-6-[(1R)-1-HYDROXYETHYL]-4-METHYL-7-OXO-1-AZABICYCLO[3.2.0]HEPT-2-ENE-2-CARBOXYLIC ACID SODIUM SALT