Pain
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Randomized Controlled Trial Controlled Clinical Trial
No evidence for the development of acute tolerance to analgesic, respiratory depressant and sedative opioid effects in humans.
It is widely accepted that chronic opioid therapy is associated with the development of pharmacological tolerance. More controversial is the question as to whether acute opioid administration can result in "acute tolerance." The aim of this double-blind, placebo-controlled study in thirty-six healthy human volunteers was to examine whether a 3-h intravenous infusion delivering two different but clinically relevant doses of the mu-opioid receptor agonist remifentanil would result in tolerance to analgesic, respiratory depressant and/or sedative opioid effects. The blood remifentanil concentration versus opioid effect relationship was determined before and after the 3-h infusion. ⋯ Neither dose of remifentanil produced detectable tolerance to any of the measured opioid effects following a 3-h infusion. The study was adequately powered to detect a decrease in potency of 5-24% for analgesia, 20-48% for respiratory depression, and 32% for sedative effects. These results suggest that short-term administration of clinically useful doses of remifentanil is not associated with the development of significant tolerance to analgesic, respiratory depressant, or sedative opioid effects.
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Randomized Controlled Trial Clinical Trial
Opposite effects of opioid blockade on the blood pressure-pain relationship in depressed and non-depressed participants.
The effect of the opioid antagonist naltrexone on the relationship between blood pressure and pain was examined in 24 participants with major depressive disorder and 31 non-depressed controls, before and after 25 min of stressful mental arithmetic. Pain was induced by immersing the non-dominant foot in 2 degrees C ice-water for as long as possible or until 4 min had elapsed (the cold pressor test). Blood pressure was measured before each cold pressor test, and at 2-min intervals during mental arithmetic. ⋯ However, naltrexone unmasked an association between blood pressure and pain--those with highest blood pressure reported least cold-induced pain. Thus, endogenous opioids apparently masked an analgesic mechanism linking elevated blood pressure with reduced sensitivity to pain in participants with major depressive disorder. Noradrenergic mechanisms involved in active coping, stress-induced analgesia and baroreflexes might account for these findings.
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Randomized Controlled Trial
The effect of attentional re-training and threat expectancy in response to acute pain.
This study aimed to investigate the efficacy of implicit attention re-training (AR) on pain ratings, threshold and tolerance during the cold-pressor task and to determine whether the effectiveness of AR was affected by threat expectancy. One hundred and four undergraduate psychology students were randomly assigned to receive either threat-alleviating or threat-inducing information about the task. Participants were then re-randomized to receive an AR that either trained them to implicitly attend to neutral and ignore pain-related stimuli (neutral training) or to attend towards pain-related stimuli (pain training). ⋯ For initial pain ratings, there was an interaction that closely approached significance (p=0.053). These results show that AR affects individual's perceptions of and their responses to pain during an experimental task in a similar way to increasing the threat expectancy of the task. Future research should trial AR in real-life settings to determine whether these results can be generalized.