The intrathecal catheter will be left in place for 32 h postoperatively to provide analgesia, and lumbar CSF (0.5 ml) will be withdrawn (0.5 mL) at 2, 4, 8, 12, 24, and 32 h after the initial oral dose. CSF will be frozen at -80 Centigrade (C) for subsequent assay of neurotransmitter levels. Even though CSF pregabalin does not reach its peak concentration until at least 8 h after an oral dose, earlier time points are important because: