Imipramine reduces experimental pain

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Abstract
In a homogeneous sample of 20 healthy male students, the analgesic effects of the tricyclic antidepressant imipramine (100 mg) were compared to those of the narcotic meperidine (150 mg) and a further tricyclic compound with assumed analgesic properties (fluradoline, 450 mg). Drugs were orally administered, using a placebo controlled, double-blind repeated measures Latin Square design. Phasic pain was induced by intracutaneous electrical shocks with random intensities and interstimulus intervals. Each stimulus block consisted of 80 stimuli and lasted for 20 min. Pain estimates, somatosensory evoked cerebral potentials (SSEPs) and power spectral density of the electroencephalogram (EEG) were measured under each drug condition. Under placebo, pain ratings and SSEP amplitudes were constant within the entire session lasting for approximately 4 h. Meperidine analgesia was evident within 30 min of drug application, reaching a maximum after about 90 min. Imipramine produced a comparable degree of pain reduction, however, with a delay of 2 h. Under both drugs, the decrease in pain ratings was accompanied by decreased amplitudes of the late components of the SSEP, as well as by a reduction in alpha activity and an enhancement of slow EEG waves. Effects of fluradoline on experimental pain could not be affirmed. These findings are discussed in terms of pain relief and decrease in vigilance.