Topical capsaicin (low concentration) for chronic neuropathic pain in adults.
Author(s): Derry S, Moore RA.
Affiliation(s): Pain Research and Nuffield Department of Clinical Neurosciences, University of
Oxford, Oxford, UK. email@example.com.
Publication date & source: 2012, Cochrane Database Syst Rev. , 9:CD010111
BACKGROUND: Topical creams with capsaicin are used to treat pain 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. There is uncertainty about the efficacy and tolerability of
capsaicin for treating painful chronic neuropathies. This is an update of an
earlier review of topical capsaicin for chronic neuropathic pain in adults that
looked at all doses and formulations of capsaicin. The original review has now
been split: here we consider only formulations using a low concentration of
capsaicin (< 1%) applied several times daily over several weeks, while another
review will consider a single application of capsaicin at a high concentration.
OBJECTIVES: To review the evidence from controlled trials on the efficacy and
tolerability of topically applied low-concentration (< 1%) capsaicin in chronic
neuropathic pain in adults.
SEARCH METHODS: Cochrane CENTRAL, MEDLINE, EMBASE and Oxford Pain Relief
Database, searched to July 2012.
SELECTION CRITERIA: Randomised, double-blind, placebo-controlled studies of at
least six weeks' duration, using low-concentration (< 1%) topical capsaicin to
treat neuropathic pain.
DATA COLLECTION AND ANALYSIS: Two review authors independently assessed study
quality and validity, and extracted data. Information was extracted on numbers of
participants with pain relief (clinical improvement) after at least six weeks,
and with local skin reactions, and used to calculate relative risk (or risk
ratio, RR) and numbers needed to treat to benefit (NNT) and harm (NNH). Details
of definition of pain relief and specific adverse events were sought.
MAIN RESULTS: No additional studies were identified for this update of low
concentration capsaicin. Included studies were published before 1996. Six studies
(389 participants in total) compared regular application of low dose (0.075%)
capsaicin cream with placebo cream. There was substantial heterogeneity in
results, probably as a result of the small number of studies each with small
numbers of participants, as well as the different pain conditions studied and
different definitions of "clinical success" reported. Only two studies reported
data for the preferred primary outcome of at least 50% pain relief, and there
were too few data for pooled analysis. Local skin reactions were more common with
capsaicin, usually tolerable, and attenuated with time; the NNH for repeated
low-dose application was 2.5 (95% confidence interval (CI) 2.1 to 3.1). All
studies satisfied minimum criteria for quality and validity, but maintenance of
blinding remains a potential problem.
AUTHORS' CONCLUSIONS: There were insufficient data to draw any conclusions about
the efficacy of low-concentration capsaicin cream in the treatment of neuropathic
pain. The information we have suggests that low-concentration topical capsaicin
is without meaningful effect beyond that found in placebo creams; given the
potential for bias from small study size, this makes it unlikely that
low-concentration topical capsaicin has any meaningful use in clinical practice.
Local skin irritation, which was often mild and transient but may lead to
withdrawal, was common. Systemic adverse effects were rare.