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 controversial. 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-induced functional-impairment model in the rat (PIFIR). Pain was produced by the intraarticular injection of uric acid in the right hind limb. Oral administration of diclofenac resulted in a dose-dependent antinociceptive effect. Oral administration of a vitamin B complex preparation containing thiamine (vitamin B(1)), pyridoxine (vitamin B(6)), and cyanocobalamin (vitamin B(12)) in 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 antinociceptive effect similar to that of diclofenac alone. On the other hand, coadministration of cyanocobalamin significantly increased diclofenac-induced antinociception. It is concluded that the potentiation of diclofenac-induced antinociception in the PIFIR model is due to cyanocobalamin.