Pain
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Evidence indicates that excitatory amino acids (EAAs) like glutamate and aspartate are important in the processing of nociceptive information in the dorsal horn of the spinal cord. Recently, the role of particular EAA receptors in pain transmission and facilitated pain states has been examined utilizing spinal administration of specific receptor antagonists. Most investigators have studied the involvement of N-methyl-D-aspartate (NMDA) EAA receptors in hyperalgesia and nociception; less is known about the importance of non-NMDA EAA receptors in animal models of persistent pain. ⋯ Intrathecal NBQX also inhibited non-evoked pain behavior. In conclusion, non-NMDA receptor antagonists produced a marked decrease in pain behaviors in this model of postoperative pain. Thus, non-NMDA receptors are important for the maintenance of short-term pain behaviors caused by an incision and drugs blocking these receptors may be useful for the treatment of postoperative pain in patients.
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Temporal summation of pain occurs when repeated stimuli become increasingly painful in spite of unchanged stimulus intensity. Summation can be quantified as the difference in pain between the first and the last stimulus in a train of stimuli. The aim of the study was to compare temporal summation of pain in normal skin with summation of pain in skin with primary and secondary hyperalgesia evoked by a heat injury. ⋯ Temporal summation at high stimulus intensities was more pronounced than at lower intensities (P < 0.0002). We found no correlation between either temporal summation and area of secondary hyperalgesia, or temporal summation and pain intensity during the induction of heat injury. We conclude that the development of primary and secondary mechanical hyperalgesia after heat injury in man was not associated with changes in temporal summation of painful electrical stimuli.
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Fillingim and Maixner (Fillingim, R. B. and Maixner, W., Pain Forum, 4(4) (1995) 209-221) recently reviewed the body of literature examining possible sex differences in responses to experimentally induced noxious stimulation. Using a 'box score' methodology, they concluded the literature supports sex differences in response to noxious stimuli, with females displaying greater sensitivity. ⋯ Given the estimated effect size of 0.55 threshold or 0.57 for tolerance, 41 subjects per group are necessary to provide adequate power (0.70) to test for this difference. Of the 34 studies reviewed by Fillingim and Maixner, only seven were conducted with groups of this magnitude. The results of this study compels to caution authors to obtain adequate sample sizes and hope that this meta-analytic review can aid in the determination of sample size for future studies.
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Randomized Controlled Trial Clinical Trial
Dose-response relationship of opioids in nociceptive and neuropathic postoperative pain.
The treatment of neuropathic pain with opioid analgesics is a matter of controversy among clinicians and clinician scientists. Although neuropathic pain is usually believed to be only slightly responsive to opioids, several studies show that satisfactory analgesia can be obtained if adequate doses are administered. In the present study, we tested the effectiveness of buprenorphine in 21 patients soon after thoracic surgery (nociceptive postoperative pain) and 1 month after surgery in the same 21 patients who developed postthoracotomy neuropathic pain with a burning, electrical and shooting quality. ⋯ In fact, if the AD50 soon after surgery was low, the AD50 increase in the long-term neuropathic pain was threefold. By contrast, if the AD50 soon after surgery was high, the AD50 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 resistance is already present in other painful conditions.
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Randomized Controlled Trial Clinical Trial
Double-blind evaluation of short-term analgesic efficacy of orally administered diclofenac, diclofenac plus codeine, and diclofenac plus imipramine in chronic cancer pain.
A prospective double-blind randomized trial was conducted on 184 cancer patients with moderate to severe chronic pain to evaluate the analgesic efficacy and tolerability of diclofenac alone (50 mg q.i.d.) or in combination with a weak opioid (codeine 40 mg q.i.d.), or with an anti-depressant (imipramine, 10 or 25 mg t.i.d.). All demographic and clinical characteristics including cancer type, presence of bone metastases, baseline pain severity, neuropathic and nociceptive pain, and depressive state, were well balanced between the three treatment groups. ⋯ Patients on imipramine plus diclofenac and on placebo plus diclofenac were withdrawn mainly for inadequate efficacy, while patients on codeine plus diclofenac discontinued equally for inadequate efficacy or adverse events. In conclusion, in a short-term evaluation the addition of a tricyclic anti-depressant or a weak opioid to diclofenac did not provide further analgesia with respect to diclofenac administration alone.