Topical salicylates useful for acute pain but show poor efficacy in chronic arthritic pain

[Guest guest]

Rheumawire

May 5, 2004

Topical salicylates useful for acute pain but show poor efficacy in

chronic arthritic pain

Oxford, UK - Topical rubefacients containing salicylates may be

efficacious in the treatment of acute pain, such as sprains, strain, and

sports injuries, but they are moderately to poorly efficacious in

chronic arthritis and rheumatic pain, concludes a systematic review in

the April 24, 2004 issue of BMJ [1]. It's the first to have been

conducted on these products.

" It has been suggested that topical analgesics owe much of their

efficacy to rubbing during application, giving a high placebo response

rate, " say researchers Dr Lorna Mason and colleagues (Oxford Radcliffe

Hospital, UK). However, the " evidence suggests otherwise. The placebo

gels were rubbed onto the skin in the same way as active treatments, and

we found that active treatments were significantly better than placebo

in double-blind clinical trials. "

They caution, however, that the results are tentative, as the clinical

trials reviewed were limited by small size, as well as inadequate design

and validity. The better trials showed little difference from placebo,

they add. Nevertheless, there is now some evidence for the use of these

products. Previous searches for trials have been hampered by a lack of

consensus on the definition of rubefacients, and some have led to the

conclusion that the only evidence was anecdotal. " It is more likely that

nobody really looked for the evidence until now, " they comment.

Mason et al explain that they defined their own outcome of clinical

success as around a 50% reduction in pain. The trials they reviewed

contained 7 types of rubefacients, found as principal ingredients in

more than 30 counterirritant preparations available in the UK through

pharmacies.

The conclusion about efficacy in acute pain was based on a review of 3

placebo-controlled clinical trials involving a total of 182 patients.

The mean treatment response rate was 67% (range 25%-90%), compared with

18% (range 0-59%) in the placebo groups. Treatment with the rubefacient

was significantly better than placebo (relative benefit 3.6, 95% CI

2.4-5.6). The number needed to treat was 2.1 (1.7-2.8) for at least 50%

pain relief at 7 days compared with placebo.

Efficacy in chronic pain was estimated from 6 placebo-controlled trials

involving a total of 429 patients. The mean treatment response rate was

54% (range 35%-80%), compared with 36% (20%-53%) in the placebo groups.

Treatment with the rubefacient was significantly better than placebo

(relative benefit 1.5, with 95%CI=1.3-1.9). The number needed to treat

was 5.3 (3.6-10.2) for at least 50% pain relief at 14 days compared with

placebo.

Local adverse events were rare, with no significant difference between

treatment and control groups, and no withdrawals due to adverse effects

were reported.

Most of the trials lasted 14 days or less, and the longest was only 28

days. " For chronic conditions in particular, information is needed on

long-term efficacy and adverse events . . . [such as] long-term effects

of continuous irritation on the skin, which may vary according to drug

and vehicle, " Mason et al comment.

The same group has also published a systematic review of topical

capsaicin products for use in chronic pain [2], as reported by

rheumawire. Both of the reviews were published in BMJ online a few weeks

before appearing in print.

In an accompanying commentary [3], Dr Tramer (University of

Geneva, Switzerland) says the information from these 2 reviews can be

put together to draw up some " pragmatic clinical guidelines. " Topical

capsaicin can be regarded as an adjuvant to standard treatment for

neuropathic pain or as a last resource when everything else has failed.

Topical salicylates and nonsteroidal anti-inflammatory drugs have few

local and systemic effects, and so these creams may be used as a

first-line treatment in, for instance, sports injuries, he suggests,

especially as they are available over the counter.

" Topical analgesics are popular among patients but do not have a good

reputation among doctors, " Tramer comments. " Many doctors are not

convinced that these creams work. " One reason may be the apparent

unreliability of the existing evidence supporting their usefulness, he

suggests, noting that there are few published trials, and most are of

low quality, questionable validity, and limited size. This is what makes

systematic reviews such as the ones conducted by Mason et al " so

valuable, " he says.

Zosia Chustecka

Sources

1. Mason L, RA, JE, et al. Systematic review of efficacy

of topical rubefacients containing salicylates for the treatment of

acute and chronic pain. BMJ 2004 Apr 24; 328(7446):995.

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

of topical capsaicin for the treatment of chronic pain. BMJ 2004 Apr 24;

328(7446):991.

3. Tramer MR. It's not just about rubbing--topical capsaicin and topical

salicylates may be useful as adjuvants to conventional pain treatment.

BMJ 2004 Apr 24; 328(7446):998.

I'll tell you where to go!

Mayo Clinic in Rochester

http://www.mayoclinic.org/rochester

s Hopkins Medicine

http://www.hopkinsmedicine.org