These experiments were repeated in parallel in the presence of ketamine (100 μM) and/or MK-801 (dizocilpine, 150 μM), APV (D-2-amino-5-phosphonovalerate, 300 μM ("low") or 3 mM ("high"), or NMDA (30 μM). The modulation of MRSA-stimulated macrophage TNF production by ketamine was subsequently examined also at a range of concentrations of 10 μΜ, 50 μΜ, 100 μΜ and 150 μΜ. The selected concentration (100 μM) is based on the achievable anesthetic concentrations [36] [37] [38] [39] and on the pre-existing literature related to ketamine's TNF suppressive effect on murine macrophage models when stimulated by LPS [23] [24] [25] 27] . The concentrations for the other factors were selected from the available literature, MK-801 [40] [41] [42] , APV and NMDA [32] have previously been studied in cell culture models and have been shown to not cause cytotoxicity at the tested concentrations. Ketamine and/or MK-801 or APV or NMDA were added to the macrophage cultures one hour prior to bacterial challenge. The source of ketamine was Ketalar ® , a racemic mixture (1:1) of optically active isomers (R and L) of this drug, purchased from the LBCH pharmacy. Emphasis in the experiment was placed on correlation with the clinical situation; thus racemic ketamine, the most commonly clinically used product, was selected. Dizocilpine (MK-801), APV and NMDA were purchased from Sigma Chemical Co. (St. Louis, MO).