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 Fifty unique studies (including three unpublished studies) were included in the analyses.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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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.