On an individual level, there is a difference in the analgesic response to a given opioid. Various factors such as gender, age, and genetic variation can affect the analgesic response. The genetic variation can influence pharmacokinetics (eg drug transporters and drug-metabolizing enzymes) and/or pharmacodynamics (eg opioid receptor and catechol-O-methyltransferase enzymes). We present recent experimentally induced pain, postoperative pain, and cancer pain and chronic non-malignant pain conditions studies in humans, focusing on the association between genetic variation and analgesic response assessed as opioid consumption or changes in pain scores. Studies have shown promising results regarding pharmacogenetics as a diagnostic tool for predicting the individual response to a given opioid in the experimental settings; however, in the clinic, it is a more complicated task to accomplish.

High-quality information on the potential benefit and harm of a drug is required for patients and clinicians to make informed treatment decisions and to enable cost-effectiveness modeling to be undertaken. This systematic review describes the collection and reporting of adverse event data as presented in published clinical trials of neuropathic pain for the evaluation of antidepressant or antiepileptic drugs. A total of 74 studies in 16,323 patients published between 1965 and 2012 were identified, of which 43 were published from 2004 onwards. The review found that methods used to collect adverse event data, the frequency of collection, and the selection criteria used by authors for reporting adverse events vary substantially, and these events are often inadequately reported. Consequently, a potential synthesis of valuable harm information across trials is hampered. We make recommendations regarding the reporting of methods used to collect, assess, select, and present adverse event data in publications. Through the Core Outcome Measures in Effectiveness Trials (COMET) initiative, core outcome sets (which include effectiveness and harm) are developed by disease condition. To facilitate data synthesis for adverse events of drug therapies, we suggest that core outcome sets for harms could be developed by therapeutic class (ie, individualized for each class of drug). To improve comparability of information across trials collection methods need to be standardized for patient reports (spontaneous or prompted) and active surveillance (clinical examinations and laboratory tests). Uniform methods for presenting summary information regarding recurrent events, duration and timing of events requires further research.

BackgroundPain tolerance is subject to considerable inter-individual variation, which may be influenced by a number of genetic and non-genetic factors. The mu, delta and kappa opioid receptors play a role in pain perception and are thought to mediate different pain modalities. The aim of this study was to explore associations between pain thresholds and gender and genetic variants in the three opioid receptor genes (OPRM, OPRD and OPRK). Experimental multi-modal pain data from previously published studies carried out in healthy Caucasian volunteers were used in order to limit the number of confounders to the study outcome. Data on thermal skin pain (n=36), muscle pressure pain (n=31) and mechanical visceral pain (n=50)) tolerance thresholds were included.ResultsNineteen genetic polymorphisms were included in linear regression modeling. Males were found to tolerate higher thermal and muscle pressure pain than females (p=0.003 and 0.02). Thirty four percent of variability in thermal skin pain was accounted for by a model consisting of OPRK rs6473799 and gender. This finding was just outside significance when correction for multiple testing was applied. Variability in muscle pressure pain tolerance was associated with OPRK rs7016778 and rs7824175. These SNPs accounted for 43% of variability in muscle pressure pain sensitivity and these findings remained significant after adjustment for multiple testing. No association was found with mechanical visceral pain.ConclusionThis is a preliminary and hypothesis generating study due to the relatively small study size. However, significant association between the opioid receptor genes and experimental pain sensitivity supports the influence of genetic variability in pain perception. These findings may be used to generate hypotheses for testing in larger clinical trials of patients with painful conditions.