Preemptive intrathecal ketamine delays mechanical hyperalgesia in the neuropathic rat

We studied the effect of preemptive intrathecal ketamine administration on the development of mechanical hyperalgesia in a rat model of mononeuropathy. Rats given intrathecal ketamine 1 mg/kg or normal saline were subsequently rendered neuropathic by placing four loose Ligatures around the sciatic nerve. The onset of resultant hyperalgesia was evaluated using von Frey monofilaments. Preemptive ketamine significantly slowed the onset of mechanical hyperalgesia at both 2.35 g (P < 0.04) and 4.19 g (P < 0.05) thresholds through the third postoperative day but did not alter the ultimate degree of hyperalgesia in either severity or frequency in this model. We conclude that ketamine delayed the onset, but failed to prevent the development of, mechanical hyperalgesia in a rat model of peripheral mononeuropathy. Implications: Pain in response to light touch may follow nerve injury. Prevention of this complication would be clinically useful. Ketamine, an anesthetic, was administered spinally to rats before nerve injury in an attempt to prevent the development of chronic pain. Hypersensitivity to light touch was delayed by preemptive ketamine.