Action of neurotropin on cold-induced pain in normal volunteers: a double-blind placebo study

The analgesic action of neurotropin, a biological compound widely used in Japan with a record of very limited side-effects, was tested in 8 Caucasian normal volunteers. For the pain test, the subjects were requested to immerse the right hand in ice-cold water and to report the appearance of the following sensations: pain threshold (PThr) and tolerance to pain (PTol). Pain sensitivity range (PSR) was calculated by difference between PThr and PTol expressed in s from beginning of immersion. Neurotropin tablets or an indistinguishable inert placebo were administered according to a randomized double-blind cross-over design and their influence in the pain test was investigated during 2 daily sessions. The effects of both treatments were assessed by calculating the difference between initial and post-medication values for each pain response parameter. Under placebo the means of all effects were found to be negative, reflecting the appearance of hyperalgesia under repetitive pain conditions, with neurotropin, the effects on PTol and PSR were positive and significantly different from those of placebo. These results are discussed in terms of possible mechanisms of action: neurotropin analgesic activity could be linked to its kinin release-inhibiting properties or to a reduction in vaso-constriction and hyperalgesia related to an effect on catecholamines.