Effect of diclofenac on the antiallodynic activity of vitamin B12 in a neuropathic pain model in the rat.

B vitamins have been used as analgesic drugs to treat pain disorders associated with their deficiency. More recently it has been claimed that B vitamins are useful to relieve different pain states as carpal tunnel, migraine and premenstrual tension. In Latin America, B vitamins are commonly used to treat neuropathic pain; however, there is no data to support this indication. In the present work we assessed the possible analgesic activity of vitamin B12 alone and combined with diclofenac in a neuropathic pain model in the rat. Neuropathic pain was induced by ligation of the left L5 and L6 spinal nerves of female Wistar rats. Tactile allodynia was determined by measuring paw withdrawal in response to probing with a series of calibrated von Frey filaments. Vitamin B12 (0.75-6 mg/kg), but not diclofenac (1-10 mg/kg), reduced in a dose-dependent manner tactile allodynia induced by spinal nerve ligation. Diclofenac (3.2 mg/kg) was not able to further increase vitamin B12-induced antiallodynia. Results indicate that vitamin B12, but not diclofenac, produces antiallodynic effects in the rat and suggest that this vitamin could be a potential treatment for neuropathic pain in humans.