Opioids in non-cancer pain: Transdermal fentanyl is effective in reducing neuropathic pain

Abstract

Recent controlled trials indicate that oral opioids attenuate neuropathic pain. We investigated the effects of transdermal fentanyl on pain, function, and cognition in patients with chronic postamputation pain, postherpetic neuralgia or small fiber neuropathy. An open-label, pre-post drug therapy design was used. Outcome measures were pain intensity (NRS 0-10), activity level, percentage pain relief (0-100%) and cognitive function. 26 adult patients (pain ≥ 3 months; pain intensity ≥3) were enrolled. The protocol consisted of a 2 week baseline period, followed by 6 weeeks of drug titration and 8 weeks of maintenance. An electronic monitor was used to record pain scores (three times a day) and activity (Actiwatch, Bend). Patients were allowed to continue their antidepressant and anticonvulsant therapy. Transdermal fentanyl was started initially at 25 mcg/hr and titrated based on pain intensity, analgesia, and adverse effects. Cognitive function was tested using the grooved peg-board and the digit symbol substitution tests. Average pain scores during the last week of pre drug phase and the post drug maintenance phase were compared in patients who had completed the study, using paired t-tests. 11 patients have completed the study at present (5- post amputation, 4-small fiber neuropathy, 2-postherpetic neuralgia). The mean age was 53± 12 years, mean pain intensity at baseline was 7.7 ± 1.3. The average reduction in pain was 3.4 ± 1.6, with 9 of 11 patients reporting ≥30% improvement in pain (p<0.0001) and 4 of 11 reporting ≥50% pain relief. There was a trend towards increased activity level with no appreciable effects on cognitive measures once on a stable dose of transdermal fentanyl. Drowsiness (4/11),vomiting (3/11) were the most common side effects. Transdermal Fentanyl significantly reduced pain intensity among patients with neuropathic pain without impairing cognition. Ongoing studies will provide information on functional improvement with transdermal fentanyl.