For the single comparison experiments (ketamine or MK 801 or APV), TNF secretion measurements were validated with an average of at least three well replicates and each of the experiments was repeated at least three times (a total of at least nine samples). The four preliminary runs and all the exposures (total of 16) where the inocula were different from 10 5 to10 7 CFUs/mL at the verifying colony count were excluded from the final analysis. Experiments with different exposure times (6, 10, 14, 24 hours) were conducted to determine whether the inhibition increased over time. In the multiple comparison experiments (ketamine and MK 801 synergistic action), TNF was measured from at least four well replicates. All experiments were performed separately for LAC and for MW2 MRSA strains. There is an intrinsic experimental variation of absolute values of TNF production (up to 25%) because of cell culture and macrophage growth characteristics.