Derry S, et al. Topical capsaicin (high concentration) for chronic neuropathic pain in adults. Cochrane Database Syst Rev. 2013;2:CD007393.
This systematic review evaluated studies involving high-concentration (8%) topical capsaicin as a single patch application for chronic neuropathic pain in adults. Scientific database searches included trials up until December 2012 and limited selection criteria to those that were randomized, double-blind, placebo-controlled studies of ≥6 weeks in duration. Data extracted included numbers of participants with pain relief after ≥6 weeks. Risk ratio and numbers needed to treat (NNT) were calculated. First-tier evidence of efficacy was considered to be long-duration pain relief, usually determined from the patient global impression of change (PGIC), most often at 8 and 12 weeks. Second-tier evidence was considered to be average pain scores over Weeks 2–8 and 2–12, and number of participants with ≥30% pain reduction or ≥50% reduction over baseline.
A total of 6 studies involving 2073 participants were reviewed, and found to be of good reporting quality. Of those, 4 studies involved 1272 participants with postherpetic neuralgia, and 2 studies involved 801 participants with HIV-neuropathy. Control for blinding was topical capsaicin 0.04%. At both Week 8 and 12, high-concentration capsaicin showed significant benefit over controls for those reporting to be much or very much better: NNT 8.8 (95% CI 5.3–26) and 7.0 (95% CI 4.6–15), respectively. More participants had average Week 2–8 and Week 2–12 pain intensity reductions ≥30% and ≥50% over baseline with active treatment than controls (NNT 10–12). In one HIV-neuropathy study, Week-12 NNT to be much or very much better was 5.8 (95% CI 3.8–12). Over both HIV-neuropathy studies more participants had average Week 2–12 pain intensity reductions over baseline of ≥30% with active treatment than controls (NNT 11) . Frequency of serious adverse events appeared to be comparable between arms: active treatment, 4.1% vs controls, 3.2%. There were no between-group differences for adverse event withdrawals, although withdrawals were somewhat more common with controls for lack of efficacy.
The reviewers concluded that high-concentration capsaicin generates higher levels of pain relief than controls for chronic neuropathic pain. But because the proportion who benefit is not large, it should likely be used when other therapies have failed, and should not be used repeatedly without substantial documented pain relief, due to unknown risks with repeated applications over long periods.
Cho JH, et al. Efficacy of a 0.1% capsaicin hydrogel patch for myofascial neck pain: a double-blinded randomized trial. Pain Med. 2012;13:965-970.
This double-blind randomized controlled trial evaluated the efficacy of a capsaicin 0.1% hydrogel patch compared with a placebo to treat chronic myofascial neck pain. A total of 61 adults with neck pain lasting ≥3 months and clinically presenting with myofascial pain syndrome were enrolled. All participants were instructed to apply one patch to each side of the neck and shoulder girdle overlying the point of maximal pain for 12 h daily throughout the 4-week study. Each participant completed 5 surveys at baseline, at 2 weeks after start of treatments, and at the conclusion of the 4-week study. Visual analog scale (VAS) was the primary outcome measure. Other measures included the Neck Disability Index (NDI), Beck's Depression inventory (BDI), Short Form 36 Korean version, and Euroqol 5-D. Of those who completed the study (n=57), mean VAS, NDI, and BDI scores were significantly decreased at Weeks 2 and 4 from start of the intervention in both groups, with no significant between-group differences in any of the outcome measures. The authors concluded that subsequent research should discern what effects relate to capsaicin treatment, the trigger point stimulation occurring during patch application, and the placebo effect.
Ellison et al. Phase III placebo-controlled trial of capsaicin cream in the management of surgical neuropathic pain in cancer patients. J Clin Oncol. 1997;15:2974-2980.
In this double-blind crossover study, 99 patients with postsurgical neuropathic pain received 8 weeks of a 0.075% capsaicin cream followed by 8 weeks of an identical-appearing placebo cream, or vice versa. Patients were instructed to apply the study or placebo cream to the painful site 4 times daily, and to complete weekly questionnaires for treatment evaluation. During the first 8-week study period, those in the capsaicin-cream arm reported substantially more skin burning, skin redness, and coughing (P<.0001 for each). However, treatment cessation for patient refusal or toxicity was comparable between arms and those using the study cream experienced substantially more pain relief after the first 8 weeks (P=.01), with an average pain reduction of 53% vs 17%. Upon completion of the 16-week study period, patients were asked which 8-week period they felt was most beneficial. Of those who responded (n=60), 60% chose the capsaicin arm, 18% chose the placebo, and 22% chose neither (P=.001). The investigators concluded that despite toxicities, there was significant preference for the study cream to manage postsurgical neuropathic pain in those who expressed an opinion.