Neuropathic pain disorders are usually characterized by spontaneous ongoing or intermittent symptoms, stimulus-evoked positive sensory phenomena, and negative sensory phenomena. Spontaneous individual subject specific phenomena are identified in the neurologic history and are quantifiable by means of self-reported neuropathic pain symptoms tools such as scales, inventories, and questionnaires. Negative and positive sensory phenomena are assessed by the neurologic bedside examination and quantitative sensory testing (QST), which refers to psychophysical tests of sensory perception during the administration of stimuli with predetermined physical properties and following specific protocols. QST is able to capture and quantify stimulus-evoked negative and positive sensory phenomena, and as such should become standard if not a critical tool in neuropathic pain research and practice. Although the advent of anatomic and functional imaging modalities is revolutionizing our understanding of the mechanisms of neuropathic pain, only by anchoring such test results to individual subjects' own perceptions via QST can they provide meaningful information about neuropathic pain, which is based on perceptual experience. To yield useful results, QST requires a cooperative subject and carefully standardized methods, including standardization of the stimulus parameters as well as the testing environment, instructions, and evaluation methods. This manuscript provides a concise review of fundamental concepts necessary for understanding the role of QST in the process of eliciting information about sensory abnormalities associated with neuropathic pain and the place of that information in analysis of pain mechanisms. Together with the companion manuscript, this review provides definitions that should help further the use of QST as a diagnostic tool as well.
Our objective was to investigate the efficacy and safety of alvimopan, a peripherally acting mu-opioid receptor (PAM-OR) antagonist, in subjects with non-cancer pain and opioid-induced bowel dysfunction (OBD), and to identify at least one treatment regimen that improves OBD. Following a 2-week baseline period, 522 subjects reporting <3 spontaneous bowel movements (SBMs)/week (with >or=25% accompanied by a sensation of incomplete evacuation, straining, or lumpy hard stools), requiring analgesia equivalent to >or=30 mg oral morphine/day were randomized to alvimopan 0.5mg twice daily (BID), 1mg once daily (QD), 1mg BID, or placebo for 6 weeks. Compared with placebo, there was a statistically and clinically significant increase in mean weekly SBM frequency over the initial 3 weeks of treatment (primary endpoint) with alvimopan 0.5mg BID (+1.71 mean SBMs/week), alvimopan 1mg QD (+1.64) and alvimopan 1mg BID (+2.52); P<0.001 for all comparisons. Increased SBM frequency and additional treatment effects, including improvements in symptoms such as straining, stool consistency, incomplete evacuation, abdominal bloating/discomfort, and decreased appetite, were sustained over 6 weeks. The most frequently reported adverse events were abdominal pain, nausea, and diarrhea, occurring more frequently in the higher dosage groups. The alvimopan 0.5mg BID regimen demonstrated the best benefit-to-risk profile for managing OBD with alvimopan in this study population, with a side effect profile similar to that of placebo. There was no evidence of opioid analgesia antagonism. Competitive peripheral antagonism of opioids with alvimopan can restore GI function and relieve OBD without compromising analgesia.
The primary efficacy endpoint for this study of gabapentin ER was not met, most likely due to the unexpectedly large placebo response. Outcomes on secondary endpoints suggest the potential efficacy of gabapentin ER QD. Gabapentin ER was well tolerated in this study. [Clinicaltrials.gov identifier NCT00335933].
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