Background: Data from previous studies suggest that botulinum toxin A has analgesic effects against peripheral neuropathic pain, but the quality of the evidence is low. We aimed to assess the safety and efficacy of repeated administrations of botulinum toxin A in patients with neuropathic pain.
Methods: We did a randomised, double-blind, placebo-controlled trial at two outpatient clinics in France (Clinical Pain Centre, Ambroise Paré Hospital, APHP, Boulogne-Billancourt, and Neurological Centre, Hôpital Dupuytren, Limoges) and one in Brazil (Neurological Department, Hospital das Clínicas da FMUSP, São Paulo). Patients aged 18-85 years with peripheral neuropathic pain were randomly assigned (1:1) by block randomisation, according to a centralised schedule, to receive two subcutaneous administrations of botulinum toxin A (up to 300 units) or placebo, 12 weeks apart. All patients and investigators were masked to treatment assignment. The primary outcome was the efficacy of botulinum toxin A versus placebo, measured as the change from baseline in self-reported mean weekly pain intensity over the course of 24 weeks from the first administration. The primary efficacy analysis was a mixed-model repeated-measures analysis in the intention-to-treat population. This trial is registered with ClinicalTrials.gov, NCT01251211.
Findings: Between Oct 2, 2010, and Aug 2, 2013, 152 patients were enrolled, of whom 68 were randomly assigned (34 per group), and 66 (37 [56%] men) were included in the primary analysis (34 in the botulinum toxin A group and 32 in the placebo group). Botulinum toxin A reduced pain intensity over 24 weeks compared with placebo (adjusted effect estimate -0·77, 95% CI -0·95 to -0·59; p<0·0001). Pain on injection was the only adverse effect reported, and occurred in 19 (56%) participants in the botulinum toxin A group and 17 (53%) of those in the placebo group (p=1·0). Severe pain was experienced by ten (29%) participants in the botulinum toxin A group and 11 (34%) in the placebo group (p=0·8).
Interpretation: Two administrations of botulinum toxin A, each of which comprised several injections, have a sustained analgesic effect against peripheral neuropathic pain. Several factors, such as the presence of allodynia and a limited thermal deficit, may be useful in predicting treatment response and should be investigated further.
Funding: Institut National de la Santé et de la Recherche Médicale (INSERM) and Fondation CNP (France).
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