2. CSF inflammatory mediators, such as Interleukin-6 (IL-6), increase as early as 3 h after start of surgery after total hip arthroplasty (7), and so it can be expected that neurotransmitter levels will also show early changes due to the TKA surgery alone. Any characterization of pregabalin effects on neurotransmitters after surgery needs to also measure these early changes in neurotransmitter levels, since later time points (e.g. 24 h) are not independent of events occurring earlier.