Pentazocine and flupirtine effects on spontaneous and evoked EEG activity

Somatosensory (SEP), auditory evoked potentials (AEP) and power spectral density of ongoing EEG (PSD) were investigated under different drug conditions: the opioid pentazocine (30 mg), the centrally acting non-narcotic analgesic flupirtine (80 mg) and placebo were administered i.v. in a double-blind cross-over study (intersession interval 7 days) with 20 healthy male subjects. Intracutaneous electrical stimuli were applied to the finger tip with randomized intensities of two- and threefold individual pain threshold. One stimulus block consisted of 80 trials. Mean values of two stimulus blocks per session were analyzed: one block before and one block 30 min after treatment. Pentazocine significantly reduced the peak-to peak amplitude of the late SEP components (N150-P240) from pretreatment to posttreatment blocks, and flupirtine diminished this amplitude to nearly the same degree. With placebo no substantial reduction was found. In contrast to these drug-induced changes in SEP, the AEP components showed no significant alterations after any treatment. The PSD under pentazocine showed a reduction of total power. This effect was mainly due to a reduced power in the alpha band. The PSD under flupirtine showed slight increases in power of theta, alpha and beta activity. Again, under placebo no changes from pretreatment to posttreatment conditions occurred. The difference in EEG change might suggest different sites of action of the two analgesics.