1-[[(6R,7R)-2-Carboxy-7-[[(2R)-[[(5-carboxy-1H-imidazol-4-yl)carbonyl]amino]phenylacetyl]amino]-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-en-3-yl]methyl]-4-(2Sulfoethyl)-pyridinium InnerSalt;[6R-[6α,7 β(R*)]]-1-[[2-Carboxy-7-[[[[(5-carboxy-1H-imidazol-4-yl)carbonyl]amino]phenylacetyl]amino]-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-en-3-yl]methyl]-4-(2Sulfoethyl)-pyridinium InnerSalt; U 63196;