Topical capsaicin: poor efficacy in musculoskeletal disorders

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Rheumawire

Mar 31, 2004

Topical capsaicin: poor efficacy in musculoskeletal disorders

Oxford, UK - A new meta-analysis of trials with topical capsaicin for

the treatment of musculoskeletal disorders such as osteoarthritis (OA)

has shown that it has poor efficacy. However, this should not preclude

its use, say the researchers, because even mild analgesia may be

beneficial for patients with chronic pain.

Dr Lorna Mason (Oxford University, UK) and colleagues report their

findings in a paper published online March 19, 2004 in BMJ [1]. Coauthor

Dr Sheena Derry tells rheumawire: " As we say in the paper, topical

capsaicin has moderate to poor efficacy in musculoskeletal and

neuropathic pain. However, for those who do not achieve adequate pain

relief with, or who are unable/unwilling to take, other analgesics,

capsaicin may provide some relief, either on its own or as adjunctive

therapy. But it would probably not be the first-line treatment for most

patients. "

Mason et al explain the rationale behind the use of capsaicin, the

compound that makes chili peppers hot. Although application of capsaicin

initially causes a sensation of itching, prickling, or burning, this is

followed by a refractory period with reduced sensitivity. After repeated

applications, persistent desensitization occurs, possibly due to

depletion of substance P, resulting in hypoalgesia.

New EULAR guidelines for the treatment of osteoarthritis of the knee,

published last year as reported by rheumawire, concluded that topical

applications such as nonsteroidal anti-inflammatory drugs (NSAIDs) or

capsaicin " have clinical efficacy and are safe. "

In the UK, capsaicin is available by prescription only, Mason et al

note, but may be present in small quantities in topical rubefacients

sold through pharmacies. To give some perspective, in England in 2002,

more than 120 000 prescriptions were for topical capsaicin (total cost

£2.2 million), out of 4.5 million prescriptions for rubefacients and

other topical antirheumatic drugs.

The researchers conducted the meta-analysis on 3 trials involving 368

patients with musculoskeletal conditions, for which topical capsaicin

was used in a 0.025% strength. The results suggest that for every 8.1

patients treated with topical capsaicin, 1 patient would achieve at

least a 50% reduction in pain who would not have done so if given

placebo. This gives a relative benefit from topical capsaicin of 1.5

compared with placebo.

They also did a separate analysis of 6 trials in 656 patients with

neuropathic pain, for which capsaicin was used at the greater strength

of 0.075%, and also found evidence of benefit.

" Topical capsaicin is better than placebo for the treatment of chronic

pain from . . . musculoskeletal disorders, " Mason and colleagues

conclude. They note that these findings agree with the results of a

large review published in 1994 [2]. However, there are some differences

between the current study and that review, they note, " the net effect

[of which] should be a more accurate, although conservative, estimate of

efficacy. "

Although it was impossible from this analysis to judge the efficacy of

capsaicin relative to other analgesics in musculoskeletal conditions,

other meta-analyses and reviews have suggested a rank order of efficacy

of topical NSAIDs, followed by rubefacients such as those containing

salicylates, and then topical capsaicin.

With regard to adverse events, for every 16 patients treated with 0.025%

capsaicin, 1 will withdraw due to an adverse event who would not have

done so if given placebo. Adverse events usually involve a burning

sensation on application, but there is some evidence that this type of

side effect diminishes with time, they say.

" Given the relatively poor efficacy of capsaicin, does it have a part to

play in pain therapy? " Mason et al wonder.

They note that most of the patients studied had moderate or severe

chronic pain, and some of the trials recruited patients only if they

were unresponsive to other treatments. " Although topically applied capsa

icin has moderate to poor efficacy in the treatment of chronic

musculoskeletal . . . pain, it may be useful as an adjunct or sole

therapy for a small number of patients who are unresponsive to, or

intolerant of, other treatments. "

" For patients with chronic moderate or severe pain, even a small

reduction in pain can be beneficial, " they conclude.

Nainggolan

Sources

1. Mason L, RA, Derry S, JE, McQuay HJ. Systematic review

of topical capsaicin for the treatment of chronic pain. BMJ

[DOI:10.1136/bmj.38042.506748.EE]. 2004 Mar 19. Available at:

http://www.bmj.com.

2. Zhang WY, Li Wan Po A. The effectiveness of topically applied

capsaicin. A meta-analysis. Eur J Clin Pharmacol 1994; 46(6):517-522.

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