Effect of transdermal opioids in experimentally induced superficial, deep and hyperalgesic pain

BACKGROUND AND PURPOSE Chronic pain and hyperalgesia can be difficult to treat with classical opioids acting predominately at the m-opioid receptor. Buprenorphine and its active metabolite are believed to act through mu-, kappa- and delta-receptors and may therefore possess different analgesic and anti-hyperalgesic effects compared with pure mu-receptor agonists, for example, fentanyl. Here, we have compared the analgesic and anti-hyperalgesic effects of buprenorphine and fentanyl. EXPERIMENTAL APPROACH Twenty-two healthy volunteers were randomized to treatment with transdermal buprenorphine (20 mu g.h(-1), 144 h), fentanyl (25 mu g.h(-1), 72 h) or placebo patches in a double-blind, cross-over experimental pain study. The experimental pain tests (phasic pain, sensitization) involved pressure at the tibial bone, cutaneous electrical and thermal stimulation, intramuscular nerve growth factor, UVB light burn injury model and intradermal capsaicin-induced hyperalgesia. Pain testing was carried out at baseline, 24, 48, 72 and 144 h after application of the drugs. KEY RESULTS Compared with placebo, buprenorphine, but not fentanyl, significantly attenuated pressure at the tibial bone as well as pressure pain in the primary hyperalgesic area induced by UVB light The two drugs were equipotent and better than placebo against cutaneous thermal pain stimulation), but failed to show significant analgesic effect to cutaneous electrical stimulation, nerve growth factor-induced muscle soreness and to capsaicin-induced hyperalgesia. CONCLUSIONS AND IMPLICATIONS Buprenorphine, but not fentanyl, showed analgesic effects against experimentally induced, bone-associated pain and primary hyperalgesia compared with placebo. These tissue-and modality-differentiated properties may reflect the variable effects of opioid drugs observed in individual patients.