We next studied the effects of a range of concentrations of ketamine and found that inhibition of macrophage TNF secretion in response to vancomycinexposed LAC or MW2 was consistently observed at concentrations of ketamine at the lowest concentration tested (10 μM) and was greater at concentrations of 50 -150 μM ( Figure 6 ). We also examined the kinetics of inhibition of macrophage TNF secretion by incubating RAW264.7 cells for 6, 10, 14, 18 and 24 hours after exposure to ketamine at a concentration of 100 μM 1 hour prior to stimulation with vancomycin-exposed LAC or MW2. We found that the magnitude of suppression of TNF secretion was similar at all times studied (Figure 7 ).