PHARMACODYNAMIC EVALUATION OF CODEINE USING TOOTH-PULP EVOKED-POTENTIALS

Pain assessment in human volunteers is difficult, and it often require s a large number of subjects to show analgesic efficacy with statistic al significance. Electrical tooth pulp stimulation elicits a painful s ensation and produces an electroencephalographic (EEG) signal that can be recorded from the scalp when precisely controlled dental stimuli a re delivered. These somatosensory evoked potentials (EP) consist of a series of peaks or waves each characterized by their polarity, latency , and amplitude. They are obtained by processing the EEG signals that occur after tooth pulp stimulation. There is good correlation between subjective pain reports and evoked potential amplitudes (N150-P250 com ponent). Thus, EP may provide a useful model for the assessment of ana lgesic activity in human volunteers. We describe an improved method fo r producing and recording tooth pulp evoked potentials in six healthy subjects. Only 16 EEG epochs were necessary to get a reproducible EP r esponse from the participants. The approach was applied to study the e fficacy of codeine (60 mg administered orally); a decrease in the evok ed potential amplitudes after codeine administration was observed. The data were consistent with results from visual analog pain ratings giv en by the subjects.