ABSTRACT
Several studies have demonstrated the presence of opioid inducible receptors on peripheral nerves and peripheral antinociceptive effects of opioids. However, the effects of peripheral opioid administration in man are controversial. Our study used a randomized, double-blind, placebo-controlled, three-way crossover design in a human model of acute inflammatory pain (heat injury). We studied 18 healthy volunteers who each received morphine locally (2 mg), morphine systemically (2 mg), or placebo on three separate study days. The subjects received morphine infiltration subcutaneously (s.c.). 1 h before heat injury (47 degrees C, 7 min) and naloxone infiltration s.c. (0.2 mg) 2.5 h after the heat injury. Hyperalgesia to mechanical and heat stimuli were examined using von Frey hairs and thermodes, and pain was rated using a visual analogue scale. The burns produced significant hyperalgesia, but local morphine infiltration neither reduced pain during the burn, nor primary or secondary hyperalgesia to mechanical and heat stimuli after the burn. In conclusion, peripherally applied morphine had no acute antinociceptive effects in this human model of acute inflammatory pain.
Subject(s)
Analgesics, Opioid/therapeutic use , Burns/drug therapy , Morphine/therapeutic use , Nociceptors/drug effects , Pain/prevention & control , Administration, Cutaneous , Adult , Cross-Over Studies , Double-Blind Method , Female , Humans , Male , Middle Aged , Naloxone , Narcotic Antagonists , Pain MeasurementABSTRACT
Riluzole modulates several transmitter systems which may be involved in nociception. Antinociceptive effects have been shown in animal studies, but there are no human data. Therefore, we have examined the acute analgesic effect of riluzole in a human model of inflammatory pain induced by a thermal injury on the distal leg (47 degrees C, 7 min, 12.5 cm2) in 20 healthy volunteers. Hyperalgesia to mechanical and heat stimuli were examined by von Frey hairs and thermodes. We used a randomized, double-blind, placebo-controlled design, and subjects received riluzole 100 mg or placebo for 2 days with a 14-day interval. The burns produced significant hyperalgesia, but riluzole had no acute analgesic effects in normal or hyperalgesic skin.
