PEARLS 252, April 2010, written by Brian R McAvoy

Clinical question
How effective is topical capsaicin for chronic neuropathic pain in adults?  

Bottom line
Six studies compared regular application of low-dose (0.075%) capsaicin cream with placebo cream; the NNT* for any pain relief over 6 to 8 weeks was 6.6 (4.1 to 17). Two studies compared a single application of high-dose (8%) capsaicin patch with placebo patch; the NNT for ³30% pain relief over 12 weeks was 12 (6.4 to 70). Local skin irritation, which is often mild and transient but may lead to withdrawal, is common. The NNH** for repeated low-dose application was 2.5 (2.1 to 3.1). Systemic adverse effects were rare. * NNT = number needed to treat to benefit 1 individual (95% confidence intervals) ** NNH = number needed to treat to cause harm in 1 individual (95% confidence intervals)

Caveat
All studies satisfied minimum criteria for quality and validity but maintenance of blinding remained a potential problem. The limited amount of data for different neuropathic conditions and inconsistent definition of outcome meant estimates for the number of participants achieving clinically useful levels of pain relief were not robust.

Context
Topical creams with capsaicin are used to treat pain resulting from a wide range of chronic conditions, including neuropathic pain. Following application to the skin, capsaicin causes enhanced sensitivity to noxious stimuli, followed by a period with reduced sensitivity and, after repeated applications, persistent desensitisation.

Cochrane Systematic Review
Derry S et al. Topical capsaicin for chronic neuropathic pain in adults. Cochrane Reviews 2009, Issue 4. Article No. CD007393. DOI: 10.1002/14651858.CD007393.pub2. This review contains 8 trials involving 1098 participants.