Pain
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Comparative Study
Comparative actions of the opioid analgesics morphine, methadone and codeine in rat models of peripheral and central neuropathic pain.
Controversy persists in relation to the analgesic efficacy of opioids in neuropathic pain. In the present study the effects of acute, subcutaneous administration of the mu-opioid receptor agonists morphine, methadone and codeine were examined in rat models of peripheral and central neuropathic pain. In the spared nerve injury (SNI) and chronic constriction injury (CCI) models of peripheral neuropathic pain, both morphine (6mg/kg) and methadone (3mg/kg) attenuated mechanical allodynia, mechanical hyperalgesia and cold allodynia for up to 1.5h post-injection (P<0.05); codeine (30mg/kg) minimally alleviated mechanical hypersensitivity in SNI, but not CCI rats. ⋯ The therapeutic window (based on antiallodynia versus ataxia) obtained for codeine, was vastly superior to that obtained with morphine or methadone in SNI and SCI rats. Furthermore, the therapeutic window for codeine in SCI rats was 4-fold greater than in SNI rats. Our results further support the efficacy of mu-opioid receptor agonists in alleviating signs of neuropathic pain in animal models of peripheral and especially central nerve injury.
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Identifying individual differences in pain is an important topic; however, little is known regarding patterns of responses across various experimental pain modalities. This study evaluated subgroups emerging from multiple experimental pain measures. One hundred and eighty-eight individuals (59.0% female) completed several psychological instruments and underwent ischemic, pressure, and thermal pain assessments. ⋯ Cluster membership was associated with demographic variables of ethnicity and sex as well as specific psychosocial variables, although cluster differences were only partially explained by such factors. These analyses revealed that groups respond differently across varied pain stimuli, and this was not related solely to demographic or psychosocial factors. These findings highlight the need for future investigation to identify patterns of responses across different pain modalities in order to more accurately characterize individual differences in responses to experimental pain.
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Comparative Study
Intraneural injection of interleukin-1beta and tumor necrosis factor-alpha into rat sciatic nerve at physiological doses induces signs of neuropathic pain.
Proinflammatory cytokines are mediators of inflammatory and neuropathic pain. Here, we investigated pain-related behavior in rats after intraneural injection of different doses of rat recombinant interleukin-1beta (rrIL-1beta) and tumor necrosis factor-alpha (rrTNF) into the sciatic nerve. Doses ranged between 0.25 and 2500pg/ml for rrIL-1beta and 0.25-250pg/ml for rrTNF. ⋯ However, this did not reflect the extent of behavioral changes. In summary, we found a bell-shaped dose-response curve for the algesic effects of rrIL-1beta and rrTNF, peaking at doses equivalent to those of endogenous cytokines released locally after nerve injury. The absence of corresponding morphological changes in nerves supports the concept of a functional effect of the cytokines at these doses.
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Meta Analysis Comparative Study
Acute pain: individual patient meta-analysis shows the impact of different ways of analysing and presenting results.
Individual patient meta-analysis using information from clinically homogeneous acute pain trials with observations over 24h was used to investigate different ways trials can be analysed and reported. There were 13 third-molar extraction trials, with 1,330 patients using rofecoxib 50mg, 303 using ibuprofen 400mg, and 570 using placebo. Pain relief scores were available at individual time points, plus time to remedication. ⋯ The distribution of pain relief was highly skewed, especially at later times, when almost no patient was average. Different cut points for pain relief (at least 25, 50 or 75% maxTOTPAR) and longer duration changed the NNT for ibuprofen compared with placebo, but less for rofecoxib, reflecting longer duration of action of rofecoxib. Reporting for each treatment group the percentage of patients with 25, 50 and 75% pain relief at various times after dose, and reporting the proportion of patients with good or complete pain relief, and inadequate pain relief, at each time point, would improve acute pain trial reporting.
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Multicenter Study Comparative Study Clinical Trial
Identification of subgroups of persons with chronic pain based on profiles on the pain stages of change questionnaire.
This study sought to identify reliable subgroups of patients with chronic pain based on profiles of subscale scores on the Pain Stages of Change Questionnaire (PSOCQ), a reliable and valid measure of individuals' readiness to adopt a self-management approach to chronic pain. The PSOCQ was administered to 633 people seeking treatment for chronic pain. Participants were predominantly White, averaged 48 years of age, about half were men, and about half reported back pain as the primary complaint. ⋯ As predicted, clusters did not differ on measures of pain, disability, or demographics. Moreover, clusters differed significantly in theoretically consistent directions by scores on the Survey of Pain Attitudes, thus demonstrating criterion related validity for the clusters. Future research should examine the utility of PSOCQ profiles, relative to individual PSOCQ scale scores alone, in predicting response to self-management treatment approaches.