Effects of graded oral doses of a new 5-hydroxytryptamine/noradrenaline uptake inhibitor (Ro 15-8081) in comparison with 60 mg codeine and placebo on experimentally induced pain and side effect profile in healthy men.

1. Ro 15-8081 (Hoffmann-La Roche, Basle, Switzerland) is a novel mixed 5-HT/noradrenaline uptake inhibitor producing potent antinociceptive effects in animal pain models. 2. In healthy man, two models with electrically and thermally induced pain, respectively, have been shown to reliably discriminate between the effects of opioid as well as of antipyretic analgesics and placebo. 3. This study investigated the effects of single oral doses of 10, 25, and 50 mg Ro 15-8081 in comparison with 60 mg codeine and placebo on threshold and tolerance to electrically induced pain and on threshold to thermally induced pain. Furthermore, the effects on psychomotor function, self-rated subjective feelings, and side effect profile were studied. 4. Twenty healthy males participated each in five experiments in which they received, in random double-blind fashion, each of the treatments. Every experiment comprised two series of measurements before and twelve after drug administration, carried out at 30 min intervals. 5. Ro 15-8081 produced marked elevations of threshold and tolerance to electrically and of threshold to thermally induced pain. The effects of all doses of Ro 15-8081 were significantly superior to those of placebo. Threshold and tolerance to electrically induced pain were not affected differently by the three doses of Ro 15-8081, whereas the threshold to thermally induced pain was elevated significantly more by 50 mg than by 10 and 25 mg Ro 15-8081. 6. Codeine 60 mg had a more rapid onset of action and greater maximal effects than Ro 15-8081.(ABSTRACT TRUNCATED AT 250 WORDS)