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Papers of the Week

Papers: 1 Feb 2020 - 7 Feb 2020

Human Studies, Pharmacology/Drug Development

2020 Sep - Oct

J Pain



Evolution of Analgesic Tolerance and Opioid-Induced Hyperalgesia over 6 months: Double-blind randomized trial incorporating experimental pain models.


Contributors to the ongoing epidemic of prescription opioid abuse, addiction, and death include opioid tolerance, withdrawal symptoms, and possibly opioid-induced hyperalgesia (OIH). Thirty stable chronic non-malignant pain patients entered a six-month long, randomized, double-blind, dose-response, two-center trial of the potent opioid levorphanol, conducted over a decade ago during an era of permissive opioid prescribing. Eleven were taking no opioids at study entry and eleven were taking between 35-122 morphine equivalents (MEQ). Five weeks titration preceded twenty weeks stable dosing. Tolerance and OIH were inferred individually based on chronic pain ratings, Brief Pain Inventory scores, and results of the Brief Thermal Sensitization (BTS) model at five opioid dosing sessions. Seventeen patients completed. The average final daily opioid dose was 132; range 14-300; average addition 105 MEQ. After observed dosing, the BTS area of hyperalgesia changed minimally but the painfulness of skin heating was reduced. Weekly 0-100 VAS pain ratings (average 64 at study entry, 48 at end titration, 45 at end stable dosing) decreased a median 19%, but eight completed with higher VAS ratings. Three completers had evidence of both tolerance and hyperalgesia. A fully-powered trial similar to this feasibility study is ethically questionable. A large-scale pragmatic trial is more realistic. Trial Registration: NCT00275249 Evolution of Analgesic Tolerance With Opioids Perspective: A double-blind, six-month, high-dose opioid feasibility trial, completed years ago, provides critically important data for clinically defining analgesic tolerance and opioid-induced hyperalgesia (OIH). Overall benefit was small, and 18% of patients had evidence of both tolerance and OIH. Future work requires a different approach than a classic RCT design.