The analgesic efficacy of flupirtine in comparison to pentazocine and placebo assessed by EEG and subjective pain ratings.

In a placebo-controlled double-blind study the analgesic efficacy of the non-narcotic analgesic flupirtine (80 mg i.v.) was evaluated in comparison with the opioid pentazocine (30 mg i.v.). The variables investigated were the subjects' pain ratings (E), the somatosensory evoked cerebral potentials (SEP), the auditory evoked potentials (AEP) and the power spectral density of the ongoing EEG (PSD). One stimulus block before (PRE) and one stimulus block after (POST) medication were applied. In one stimulus block 80 intracutaneous electrical stimuli of two- and three-fold pain threshold amperage were given in randomized order of intensity and inter-stimulus intervals. Both treatments reduced the subjects' pain ratings significantly, while the placebo values were constant. These effects on pain ratings were in parallel with the SEP changes. The peak-to-peak amplitudes of the late components were significantly diminished by both drugs. Placebo had no effect on this variable. The AEPs remained considerably constant after all three treatments indicating specific drug effect on the pain-related somatosensory pathways. Flupirtine showed effects similar to those of pentazocine in terms of pain relief. The changes in ongoing EEG activity, however, were of a different kind. Pentazocine changed the EEG in an opiate-like manner, while flupirtine increased relative power in the theta and beta range.