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Objective: After surgical procedures, anesthesia itself may affect pain perception. Particularly, there is increasing evidence that opioids not only have analgesic effects but also provoke pronociceptive changes, that is, opioid-induced hyperalgesia. We investigated the effect of different anesthetic regimens on pain processing in volunteers using a transdermal electrical pain model. In this model, stimulation of epidermal nerve fibers representing mainly peptidergic C-nociceptors leads to secondary hyperalgesia and habituation to the stimulus., Methods: Forty-eight healthy volunteers underwent conditioning noxious stimulation (CS) over 5 days. On day 2, the volunteers were randomized into 4 groups: control group (no anesthesia) and 3 groups receiving anesthesia before CS in anesthetic doses: propofol (P), propofol/remifentanil (PR), and propofol/remifentanil/S-ketamine (PRK). Quantitative sensory testing was performed on days 1 through 5 and on day 22., Results: In every group, CS was associated with short- and long-term habituation to the electrical stimulus. Repetitive CS resulted in unmodified short-term sensitization with stable areas of hyperalgesia. Although the PR group showed a trend toward increased areas of hyperalgesia on day 2, no significant differences were detectable between the groups. In contrast, anesthesia resulted in decreased intensity of the electrically evoked pain on day 2. Finally, the mechanical pain threshold before CS on day 5 was increased in all groups and remained elevated 3 weeks after the first CS, consistent with a long-term antinociceptive effect after CS., Conclusions: The results suggest a short-term analgesic effect of general anesthesia. Furthermore, the conditioning stimulation over several days induced differential modulation of pro- and antinociceptive systems., (© 2015 World Institute of Pain.)

Despite the increasing clinical use of transdermal buprenorphine, questions have persisted about the possibility of a ceiling effect for analgesia, its combination with other μ-opioid agonists, and the reversibility of side effects. In October 2008, a consensus group of experts met to review recent research into the pharmacology and clinical use of buprenorphine. The objective was to achieve consensus on the conclusions to be drawn from this work. It was agreed that buprenorphine clearly behaves as a full μ-opioid agonist for analgesia in clinical practice, with no ceiling effect, but that there is a ceiling effect for respiratory depression, reducing the likelihood of this potentially fatal adverse event. This is entirely consistent with receptor theory. In addition, the effects of buprenorphine can be completely reversed by naloxone. No problems are encountered when switching to and from buprenorphine and other opioids, or in combining them. Buprenorphine exhibits a pronounced antihyperalgesic effect that might indicate potential advantages in the treatment of neuropathic pain. Other beneficial properties are the compound's favorable safety profile, particularly in elderly patients and those with renal impairment, and its lack of effect on sex hormones and the immune system. The expert group agreed that these properties, as well as proven efficacy in severe pain and favorable tolerability, mean that buprenorphine can be considered a safe and effective option for treating chronic cancer and noncancer pain., (© 2010 World Institute of Pain.)