Characterization of the potentiation of the antinociceptive effect of diclofenac by vitamin B complex in the rat

The role of vitamin B complex preparations as an analgesic adjuvant is cont roversial. Therefore, the purpose of the present study was to characterize the potentiation of the antinociceptive effect of diclofenac by a vitamin B complex preparation and its individual components by using the pain-induce d functional-impairment model in the rat (PIFIR). Pain was produced by the intraarticular injection of uric acid in the right hind limb. Oral administ ration of diclofenac resulted in a dose-dependent antinociceptive effect. O ral administration of a vitamin B complex preparation containing thiamine ( vitamin B-1), pyridoxine (vitamin B-6), and cyanocobalamin (vitamin B-12) i n a 1:1:0.01 proportion did not produce any antinociception by itself, but it significantly potentiated the effect of diclofenac. Coadministration of diclofenac with either thiamine or pyridoxine resulted in an antinociceptiv e effect similar to that of diclofenac alone. On the other hand, coadminist ration of cyanocobalamin significantly increased diclofenac-induced antinoc iception. It is concluded that the potentiation of diclofenac-induced antin ociception in the PIFIR model is due to cyanocobalamin. (C) 2000 Elsevier S cience Inc. All rights reserved.