Pain
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Review Meta Analysis
Do sex differences exist in opioid analgesia? A systematic review and meta-analysis of human experimental and clinical studies.
Although a contribution of sex in opioid efficacy has garnered much attention, the confirmation and direction of any such difference remain elusive. We performed a systematic review of the available literature on sex differences in μ and mixed μ/κ opioid effect on acute and experimental pain. Fifty unique studies (including three unpublished studies) were included in the analyses. ⋯ Female patients had greater μ/κ opioid analgesia (n=7, effect size 0.84; 95% c.i. 0.25-1.43, P=0.005), but no sex-analgesia association was present in experimental studies (n=7). Sex differences exist in morphine-induced analgesia in both experimental pain studies and clinical PCA studies, with greater morphine efficacy in women. The data on non-morphine μ and mixed μ/κ-opioids are less convincing and require further study.
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Randomized Controlled Trial Clinical Trial
Predicting the analgesic effect to oxycodone by 'static' and 'dynamic' quantitative sensory testing in healthy subjects.
The large inter-individual variability in the magnitude of analgesia in response to opioids and the high prevalence of adverse events associated with their use underline the clinical importance of being able to predict who will or will not respond to opioid treatment. The present study used both static and dynamic quantitative sensory testing (QST) on 40 healthy volunteers in order to test whether this methodology can predict the analgesic effects of oral oxycodone, as compared to a placebo, on latency to onset, pain intensity, and tolerance to the cold pressor test (CPT). Static QST consisted of measuring heat and cold pain thresholds. ⋯ The static QST results showed that heat pain thresholds predicted the magnitude of reduction in pain intensity in response to oxycodone treatment (F((1,22))=5.63, p=0.027, R(2)=0.17). The dynamic QST results showed that TS predicted the effect of oxycodone on the tolerance to CPT (F((1,38))=9.11, p=0.005, R(2)=0.17). These results suggest that both static and dynamic QST have the potential to be useful in the prediction of the response to opioid treatment.
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Randomized Controlled Trial Clinical Trial
Deciphering the role of endogenous opioids in high-frequency TENS using low and high doses of naloxone.
Previous human studies have shown that the analgesic effect of high-frequency TENS could not be reversed by low doses of naloxone. The aim of the present study was to reinvestigate the possible contribution of opioid receptors to high-frequency TENS analgesia by using low (0.02 mg/kg) and high (0.14 mg/kg) doses of naloxone. Naloxone (high and low doses) and saline were administered intravenously to young healthy adults using a triple-blind randomized cross-over design. ⋯ However, when a high dose of naloxone was administered, TENS analgesia was completely blocked (p=.20). These results suggest that high-frequency TENS involves opioid receptors. An insufficient amount of opioid antagonist likely prevented previous human studies from discovering the importance of opioid receptors in producing high-frequency TENS analgesia.
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Comparative Study
Temporal daily associations between pain and sleep in adolescents with chronic pain versus healthy adolescents.
Adolescents with chronic pain frequently report sleep disturbances, particularly short sleep duration, night wakings, and poor sleep quality. Prior research has been limited by assessment of subjectively reported sleep only and lack of data on daily relationships between sleep and pain. The current study utilized multilevel modeling to compare daily associations between sleep and pain in adolescents with chronic pain and healthy adolescents. ⋯ The interaction between nighttime sleep efficiency and study group was significant, with adolescents with pain showing stronger associations between sleep efficiency and next-day pain than healthy participants (p=.05). Contrary to hypotheses, daytime pain did not predict nighttime sleep. Daily associations between pain and sleep suggest that further work is needed to identify specific adolescent sleep behaviors (e.g., compensatory sleep behaviors) that may be targeted in interventions.
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There exists currently a fair degree of introspection in the pain research community about the value of animal research. This review represents a defense of animal research in pain. ⋯ Finally, we discuss recent developments in animal models of pain that should improve the relevance and translatability of findings using laboratory animals. We believe that pain research using animal models is a continuing necessity-to understand fundamental mechanisms, identify new analgesic targets, and inform, guide and follow up human studies-if novel analgesics are to be developed for the treatment of chronic pain.