Long-term effectiveness of topical analgesics

Background Neuropathic pain consistently presents a significant therapeutic challenge. Topically applied analgesics have the advantage of showing low systemic side effects, but data on long-term effectiveness are lacking. Consequently, interviews were carried out with all patients being treated with topical analgesics in hospital. Methods Ethics 16-5690, German Clinical Trials Register (DRKS) 00011877. Between 2008 and 2017 a total of 265 patients were treated at least once with either capsaicin 8% (C), lidocaine 5% (L) and/or perineural botulinum toxin type A (B). From this sample, 205 patients (77%) were interviewed by telephone for feedback on pain reduction (first/last treatment: low/moderate/very good), the possible reduction of analgesic prescription and if applicable the reasons for discontinuation of use (time of interview C: 26 & x202f;+/- 19 months, L: 61 & x202f;+/- 23 months, B: 11 & x202f;+/- 6 months after start). Further pretreatment data and diagnoses were obtained from the in-house documentation system. Responders or long-term responders were defined as patients with at least one moderate pain reduction after the first or last treatment, as long as the effect was adequately maintained. Results In all treatment groups (56 & x202f;+/- 13 years, 62% male, C: 80, L: 84, B: 58 patients) patients with a long history of pain (C: 60 & x202f;+/- 73 months, L: 59 & x202f;+/- 66 months, B: 67 & x202f;+/- 71 months) and high pain intensity (numeric rating scale, NRS, C: 7 & x202f;+/- 2, L: 7 & x202f;+/- 2, B: 6 & x202f;+/- 2), were predominant. The highest primary and long-term responder rates were exhibited by L (57%/60%, B: 52%/37%, C: 23%/15%). With B, long-term responders were most frequently able to reduce analgesic use (74%, C: 58%, L: 38%). Discussion Despite the long duration of the disease, the most used off-label topical drugs L and B demonstrated a high primary response rate (in contrast to C), with most benefiting from long-term treatment.