DOSE-RESPONSE RELATIONSHIP OF OPIOIDS IN NOCICEPTIVE AND NEUROPATHIC POSTOPERATIVE PAIN

The treatment of neuropathic pain with opioid analgesics is a matter o f controversy among clinicians and clinician scientists. Although neur opathic pain is usually believed to be only slightly responsive to opi oids, several studies show that satisfactory analgesia can be obtained if adequate doses are administered. In the present study, we tested t he effectiveness of buprenorphine in 21 patients soon after thoracic s urgery (nociceptive postoperative pain) and 1 month after surgery in t he same 21 patients who developed postthoracotomy neuropathic pain wit h a burning, electrical and shooting quality. According to a double-bl ind randomized study, the analgesic dose (AD) of buprenorphine needed to reduce the long-term neuropathic pain by 50% (AD(50)) was calculate d and compared to the AD(50) in the immediate postoperative period. We found that long-term neuropathic pain could be adequately reduced by buprenorphine. However, the AD(50) in neuropathic pain was significant ly higher relative to the AD(50) in the short-term postoperative pain, indicating a lower responsiveness of neuropathic pain to opioids. We also found a strict relationship between the short-term and long-term AD(50), characterized by a saturating effect. In fact, if the AD(50) s oon after surgery was low, the AD(50) increase in the long-term neurop athic pain was threefold. By contrast, if the AD(50) soon after surger y was high, the AD(50) in neuropathic pain was only slightly increased . This suggests that, though neuropathic pain is indeed less sensitive to opioids, in some neuropathic patients a large amount of opioid res istance is already present in other painful conditions. (C) 1998 Inter national Association for the Study of Pain. Published by Elsevier Scie nce B.V.