Prolonged-release oxycodone enhances the effects of existing gabapentin therapy in painful diabetic neuropathy patients

Background: Neuropathic pain remains one of the most challenging pain syndromes; under-diagnosed, poorly managed and associated with significant co-morbidity. With standard therapeutic treatments, responders rarely exceed 50% pain relief and the majority suffer from residual pain. Titration to optimum dose is often limited by dose-related adverse events. Aims: This randomized, double-blind, placebo-controlled study assessed the potential benefit of adding oxycodone (OxyContin (R) tablets) to gabapentin. The primary endpoint was to evaluate the analgesic efficacy of co-administration of gabapentin and. prolonged-release oxycodone, whilst also evaluating the use of escape medication, sleep quality and global assessment of pain. Methods: Three hundred and thirty eight patients with moderate to severe painful diabetic neuropathy despite receiving their maximum tolerated dose of gabapentin, had oral prolonged-release oxycodone or placebo tablets added to their therapy for up to 12 weeks. Results: Oxycodone-gabapentin reduced pain score by 33% from baseline to end of treatment. The overall treatment effect was greater with oxycodone gabapentin than with placebo-gabapentin (P = 0.007). Oxycodone-gabapentin also significantly improved pain relief vs gabapentin alone (P = 0.003). Oxycodone-gabapentin co-administration was associated with less escape medication use (P = 0.03) and fewer nights of disturbed sleep (P < 0.05). Discontinuations due to lack of therapeutic effect were much lower (14% vs 54%) with oxycodone-gabapentin. The commonly seen opiate-induced adverse events were not exacerbated by the combination of oxycodone and gabapentin. Conclusions: This study provides the first evidence that co-administration of prolonged-release oxycodone and existing gabapentin therapy has a clinically meaningful effect in painful diabetic neuropathy. (C) 2007 European Federation of Chapters of the International Association for the Study of Pain. Published by Elsevier Ltd. All rights reserved.