The effects of vitamin B12 and diclofenac and their combination on cold and mechanical allodynia in a neuropathic pain model in rats.

The present study was performed to investigate the effects of long-term intraperitoneal (IP) injection of vitamin B12 and diclofenac in separate and combined treatments on cold and mechanical allodynia in a neuropathic pain model in rats. Neuropathic pain was induced by crush injury in right tibial nerve. Acetone spray and von Frey tests were used to obtain cold and mechanical allodynia responses, respectively, on day 11 after nerve crush. Normal saline, vitamin B12 and diclofenac were injected intraperitoneally for 10 consecutive days after surgery. Normal saline treated rats showed cold and mechanical allodynia responses after nerve crush. Vitamin B12 at doses of 50, 100 and 200 µg kg(-1) and diclofenac at a dose of 2 mg kg(-1) produced antiallodynic effects. Antiallodynic effects were not observed when subanalgesic doses of vitamin B12 (25 µg kg(-1)) and diclofenac (0.25 mg kg(-1)) were used together. By increasing the dose of vitamin B12 to an effective dose (100 µg kg(-1)), antiallodynic effects were observed when compared with diclofenac (0.25 mg kg(-1)) alone. The results indicated that vitamin B12 and diclofenac produced neuropathic pain suppressing effects. Moreover, a potentiation effect was observed between vitamin B12 and diclofenac.