The Effect of an Intraperitoneal Injection of Ketamine and Ketorolac on Mechanical Allodynia in Rats with Spinal Nerve Ligation

Kim, Tae Kwan; Kim, Yee Suk; Yoon, Jun Ro; Han, In Soo; Kim, Jin Seo; Lee, Chul Woo

Abstract

BACKGROUND
It is difficult to manage the symptoms of neuropathic pain, especially alloynia. The mechanism of the induction and maintenance of mechanical allodynia has been extensively researched for several decades. N-methyl-D-aspartate (NMDA) receptor antagonists are known to reduce mechanical allodynia. Recently, the role of prostaglandins in spinal nociceptive processing has been the focus of attention. Therefore, the present study was designed to investigate the effect of a combination of ketamine, a non-competitive NMDA antagonist, and of ketorolac, non-selective cyclooxygenase (COX) inhibitor on mechanical allodynia.
METHODS
Male SD rats were prepared by tightly ligating the left L5 and L6 spinal nerves. All rats developed mechanical allodynia 7 days after surgery. N group (control, n = 6) received 5 ml of 0.9% normal saline intraperitoneally. K group (n = 6) received ketamine 1 mg/kg. T group received ketorolac 30 mg/kg, and KT group received ketamine 1 mg/kg and ketorolac 30 mg/kg simultaneously. Paw withdrawal thresholds to von Frey hairs were measured before and at 15 min, 30 min, 60 min and 120 min after drug administration.
RESULTS
Normal saline and ketamine 1 mg/kg did not increase the paw withdrawal threshold from baseline. Ketorolac 30 mg/kg increased the paw withdrawal threshold only at 120 min after intraperitoneal injection. However, the co-administration of ketamine 1 mg/kg and ketorolac 30 mg/kg increased the paw withdrawal threshold significantly from baseline for 120 min.
CONCLUSIONS
Intraperitoneal injection of ketamine and ketorolac attenuated the mechanical allodynia developed by spinal nerve ligation. Therefore, we suggest that combination of ketamine and ketorolac might be useful for the management of neuropathic pain.