The effect of diazepam on nociception in mice.

The antinociceptive properties of diazepam were evaluated in mice, using four different pain tests and different doses of the drug (0.2, 0.5, 1.0 and 2.0 mg/kg). In the tail flick test and the increasing temperature hot plate test there were no effects. In the formalin test reduced licking was observed for the highest dose of diazepam. However, this dose also induced clear sedation possibly causing the reduced licking response. In the constant temperature hot plate test a hyperalgesia was found for all doses tested. This hyperalgesia was not observed in animals adapted to the test apparatus, suggesting that the "hyperalgesic" effect of diazepam may be due to reduced stress analgesia. The serum concentrations of the drug were comparable to therapeutic levels in humans. It was concluded that the sedative and anxiolytic effects of diazepam may influence the results of nociceptive tests, but the drug has probably no effect on nociception in itself.