A COMPARISON OF THE ANTINOCICEPTIVE EFFECTS OF IMIPRAMINE, TRAMADOL AND ANPIRTOLINE

1 The pain relieving properties of imipramine (100 mg orally), tramado l (150 mg orally), and anpirtoline (60 mg orally) were compared in 16 healthy subjects in a cross-over, double-blind, randomized, and placeb o-controlled study. Anpirtoline exhibits analgesia which is possibly m ediated via serotoninergic pathways, whereas tramadol exerts its effec ts at opioid receptors. The pain-relieving effect of the tricyclic ant idepressant imipramine may involve both serotoninergic and opioid mech anisms. 2 Chemo-somatosensory event-related potentials (CSSERP) were r ecorded after painful stimulation of the nasal mucosa with carbon diox ide. Subjects rated the perceived intensity of the stimuli by means of a visual analogue scale. In addition, acoustically evoked responses w ere recorded, the spontaneous EEG was analyzed in the frequency domain , the subjects' vigilance was assessed in a tracking task, and side ef fects of the drugs were monitored. 3 Anpirtoline and tramadol produced a decrease of both CSSERP amplitudes and subjective estimates of pain , the effects of the former compound being greater. In contrast, after administration of imipramine no change of CSSERP amplitudes could be detected, whereas the subjective estimate of pain intensity decreased significantly. This was accompanied by a significant decrease of arous al indicating that pain relief produced by acute administration of imi pramine was primarily related to its sedation action. 4 The analgesic properties of anpirtoline were demonstrated in man. Tramadol was chara cterized as a weak opioid analgesic. In contrast, imipramine appeared to produce its pain-relieving effects predominantly by non-specific ac tions. It is hypothesized that different analgesics may change ERP sou rces in a drug-specific manner.