Do the B-vitamins exhibit antinociceptive efficacy in men? Results of a placebo-controlled repeated-measures double-blind study.

Additive analgesic effects of long-term application of a combination of the vitamins B1, B6, B12 (thiamine diphosphate 100 mg, pyridoxsine-HCl 200 mg, cyanocobalamin 20 micrograms, p.o.) on a single dose of the nonsteroidal anti-inflammatory drug (NSAID) diclofenac (diclofenac-Na, 50 mg, p.o.) were investigated with a noninflammatory experimental pain model in 38 healthy volunteers. B-vitamins were given with 3 dosages/day for 1 week. Then experimental sessions of 3 h followed to test the analgesic efficacy of the NSAID. In these sessions, phasic pain was induced by intracutaneously applied brief electrical pulses (20 ms). Measured were the pain ratings, the cerebral potentials and the EEG delta power in responses to the stimuli as target variables for the analgesic test. Unspecific effects upon the vigilance system were evaluated by spontaneous EEG, auditory-evoked potentials and reaction times. The investigation was performed as a placebo-controlled, double-blind cross-over study. Blood samples were taken to monitor the plasma concentrations of the active agents. Whereas in the first block of stimuli (40-60 min after diclofenac medication) no analgesic effects of diclofenac could be observed, either given alone or after pretreatment with the B-vitamins, in the second stimulus block (100-120 min after medication) significant effects appeared in all target variables describing analgesia. Pain ratings were decreased by about 5%, late cerebral potentials by about 9% and stimulus-induced delta power of the EEG by about 14%. These effects were significant (p < 0.05, p < 0.01) against those under placebo, but came out to be independent of the B-vitamin pretreatment. No B-vitamin effects of the B-vitamins could be detected, either additive analgesic effects on diclofenac analgesia or on the concomitant variables describing unspecific sedative effects. Clearly the B-vitamin pretreatment for 1 week enlarged the plasma levels for vitamin B6 by 700%, for vitamin B1 by 70% and for vitamin B12 by 50%. All B-vitamin concentrations were independent of each other.