Topical 2% amitriptyline and 1% ketamine in neuropathic pain syndromes - A randomized, double-blind, placebo-controlled trial

Background: A double-blind, randomized, placebo-controlled 3-week study evaluated the efficacy of topical 2% amitriptytine, 1% ketamine, and a combination of both in treating patients with neuropathic pain. Methods: Ninety-two patients with diabetic neuropathy, postherpetic neuralgia, or postsurgical/posttramnatic neuropathic pain with allodynia, hyperalgesia, or pinprick hypesthesia were randomly assigned to receive one of four creams (placebo, 2% amitriptyline, 1% ketamine, or 2% amitriptyline-1% ketamine combined). The primary outcome measure was change in average daily pain intensity (baseline week vs. final week) using an 11-point numerical pain rating scale. Secondary outcomes included the McGill Pain Questionnaire, measures of allodynia and hyperalgesia, and patient satisfaction. Results: A reduction in pain scores of 1.1-1.5 units was observed in all groups, and there was no difference between groups. Blood concentrations revealed no significant systemic absorption. Minimal side effects were encountered. Conclusion: This randomized, placebo-controlled trial examining topical 2% amitriptyline, 1% ketamine, and a combination in the treatment of neuropathic pain revealed no difference between groups. Optimization of doses may be required, because another study has revealed that higher concentrations of these agents combined do produce significant analgesia.