Effect of minocycline on lumbar radicular neuropathic pain: A randomized, placebo-controlled, double-blind clinical trial with amitriptyline as a comparator

BACKGROUND:: Less than 50% of patients experience sufficient pain relief with current drug therapy for neuropathic pain. Minocycline shows promising results in rodent models of neuropathic pain but was not studied in humans with regard to the treatment of neuropathic pain. METHODS:: In this randomized, double-blind, placebo-controlled clinical trial, patients with subacute lumbar radicular pain received placebo, amitriptyline 25 mg, or minocycline 100 mg once a day (n = 20 per group) for 14 days. Primary outcome measure was the pain intensity in the leg as measured by a numeric rating scale ranging from 0 to 10 on days 7 and 14. Secondary outcome measures were the reduction of neuropathic pain symptoms in the leg as determined with a neuropathic pain questionnaire, consumption of rescue medication, and adverse events on days 7 and 14. RESULTS:: Sixty patients were randomized and included in an intention-to-treat analysis. After 14 days, patients in the minocycline and amitriptyline groups reported a reduction of 1.47 (95% confidence interval, 0.16-2.83; P = 0.035) and 1.41 (95% confidence interval, 0.05-2.78; P = 0.043), respectively, in the numeric rating scale compared to the placebo group. No differences were seen in the neuropathic pain questionnaire values at any time point during treatment between the three groups. The rate of adverse events in the amitriptyline group was 10% versus none in the minocycline and placebo groups. No differences were noted in the consumption of rescue medication. CONCLUSIONS:: Although both groups differed from placebo, their effect size was small and therefore not likely to be clinically meaningful.