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Topical capsaicin for chronic pain

 

Clinical bottom line

In neuropathic conditions with six trials (656 patients), topical capsaicin (0.075%) was better than placebo with an NNT of 5.7 (95% CI 4.0 to 10).

In musculoskeletal conditions with three trials (368 patients) topical capsaicin (0.025% or plaster) was better than placebo with an NNT of 8.1 (4.6 to 34).

About one third of patients experienced local adverse events with capsaicin, who would not have done so with placebo.


Background

Capsaicin is the active compound present in chilli peppers, responsible for making them hot when eaten. It binds to nociceptors in the skin, causing an initial excitation of the neurones and a period of enhanced sensitivity to noxious stimuli, usually perceived as itching, pricking or burning sensations. This is followed by a refractory period with reduced sensitivity and, after repeated applications, persistent desensitisation. It is the ability of capsaicin to desensitise nociceptors that is exploited for therapeutic pain relief.

For post-herpetic neuralgia and diabetic neuropathy, treatment is with 0.075% cream three to four times daily for eight weeks (followed by review) and for osteoarthritis treatment is with 0.025% cream, four times daily. Capsaicin is available in the UK on prescription only, but may be present in small quantities in topical rubefacients sold through pharmacies. According to the Prescription Cost Analysis, there were over 120 000 prescriptions for topical capsaicin in England in 2002, at a total cost of 2.2 million, out of a total of 4.5 million prescriptions for rubefacients and other topical antirheumatic drugs.

Reference


L Mason, RA Moore, S Derry, JE Edwards, HJ McQuay. Systematic review of topical capsaicin for the treatment of chronic pain. BMJ 2004 328: 991-994.


Systematic review

Extensive searches looked for randomised, active or placebo-controlled trials in adult patients experiencing chronic pain from either neuropathic (diabetic neuropathy, postherpetic neuralgia, polyneuropathy other neuropathies or chronic post-operative pain) or musculoskeletal (arthritic disorders, back pain, other chronic muscle pain or fibromyalgia) disorders. Application of treatment had to be 3-4 times daily, in accordance with manufacturers' instructions, and at least ten patients had to be randomised to each treatment group.

Results

Capsaicin was significantly better than placebo for neuropathic and musculoskeletal pain, though with wide dispersion in results of individual (small) trials (Figure 1).

Figure 1: Trials of topical capsaicin in musculoskeletal (red) and neuropathic pain (blue)

Neuropathic pain

Results in neuropathic pain at four and eight weeks are shown in Table 1. The mean treatment response at eight weeks was 60%, while the response to placebo was 42%. The NNT compared to placebo at eight weeks was 5.7 (4.0 to 10).

Musculoskeletal pain

Results in musculoskeletal pain at four weeks are shown in Table 1. The mean treatment response at four weeks was 38%, while the response to placebo was 25%. The NNT compared to placebo at eight weeks was 8.1 (4.6 to 34).

Table 1: Results for topical capsaicin in chronic pain

Success with
Trials
Patients
Treatment
Placebo
RB (95% CI)
NNT (95% CI)
Efficacy in neuropathic pain
efficacy at 4 weeks
4
313
91/159
64/154
1.4 (1.1 to 1.7)
6.4 (3.8 to 21)
efficacy at 8 weeks
6
656
197/331
136/325
1.4 (1.2 to 1.7)
5.7 (4.0 to 10)
Efficacy in musculoskeletal pain
efficacy at 4 weeks
3
368
70/186
46/182
1.5 (1.1 to 2.0)
8.1 (4.6 to 34)
 
Trials
Patients
Treatment
Placebo
RR (95% CI)
NNH (95% CI)
Combined adverse events
local AE
7
490
137/252
35/238
3.6 (2.6 to 5.0)
2.5 (2.1 to 3.1)
AE related withdrawals
9
901
59/456
12/445
4.0 (2.3 to 6.8)
9.8 (7.3 to 15)

 

Adverse events

Local adverse events occurred more frequently with capsaicin cream than with placebo, with a number needed to harm of 2.5 (2.1 to 15). Over half (54%) of patients had a local adverse event with capsaicin creams, and 13% of patients withdrew because of adverse events.

Comment

Topical capsaicin can be distinguished from placebo in both neuropathic pain and in musculoskeletal pain. However, estimates of efficacy are low, and adverse event rates high. Topical capsaicin in an unlikely first or even second choice for treatment, but will help some people.