Salicylate rubefacients for musculoskeletal pain in adults

The Elf popped into the local Woodland pharmacy this week and was chatting to the pharmacist about the wide range of foams, gels, lotions, and ointments containing medicines. These products are called topical medication and are applied to body surfaces such as the skin.

Some of these products contain rubefacients. These are drugs that cause irritation and reddening of the skin due to increased blood flow. They are believed to relieve pain in musculoskeletal conditions and are available on prescription and in over-the-counter remedies.

The Elf wondered if there is any evidence that these are effective? The authors of a recently updated Cochrane review looked for evidence about the usefulness of topical rubefacients containing salicylate a commonly used rubefacient. Let’s see what they found.

Here’s what they did

They searched electronic databases (to August 2014) for studies in any language for randomised controlled trials using the Oxford Quality Score as the basis for inclusion, limiting inclusion to studies that were randomised and double-blind as a minimum. Authors reviewed studies independently.

They defined musculoskeletal pain as acute painful conditions like strains and sprains, or chronic painful conditions like osteoarthritis.

Studies must have had at least 10 participants per treatment arm, and reporting outcomes at close to 7 (minimum 3, maximum 10) days for acute conditions and 14 (minimum 7) days or longer for chronic conditions.

They looked for ’clinical success’, defined as a 50% reduction in pain, measured on a visual analogue scale (VAS) or numerical rating scale (NRS), or an equivalent measure such as a “very good” or “excellent” global assessment of treatment, or “none” or “slight” pain on rest or movement, measured on a categorical scale (or similar wording) .

Here’s what they found

17 studies were included in the qualitative synsthesis and 16 in the quantatitive synthesis (meta-analysis).
Clinical success (50% re- duction in pain) at seven days for salicylates compared with placebo
- acute conditions: For every 1000 people using rubefacients only 640 had improved pain and for evey 1000 not using rubefacients 335 had improved pain. The RR (Risk Ratio) was 1.9 (95% CI 1.5 to 2.5) and the NNT (Numbers Needed to Treat) was 3.2 (2.4 to 4.9) (very low quality evidence).
- chronic conditions: For every 1000 people using rubefacients only 447 had improved pain and for evey 1000 not using rubefacients 284 had improved pain. The RR was 1.6 (1.2 to 2.0) and the NNT was 6.2 (4.0 to 13) (very low quality evidence).
Adverse events were more common with salicylate than with placebo but most of the events occurred in only two studies.

The authors concluded

There is no good evidence that topical salicylate-containing rubefacients give useful pain relief

The Musculoskeletal Elf’s view

The authors of this review report Risk Ratios (RR) and Number Needed to Treat (NNT). So let’s have a more detailed look at what these mean.

Risk ratio is used to statistically compare the risk in two different groups of people. In this review for acute pain RR was 1.9 (95% CI 1.5 to 2.5) and for chronic conditions it was 1.6 (1.2 to 2.0). At first this would appear to be statistically significant in favour of rubefacients as the RR value is greater than 1.

The authors also report the NNT the number of people who need to take the treatment for one person to benefit from the treatment. For acute pain this was 3.2 (2.4 to 4.9) and for chronic conditions this was 6.2 (4.0 to 13). Again this would appear to favour rrubefacients.

However this review also identified that all included studies were potentially at risk of bias, and there were substantial differences between studies in terms of the participants (for example the level of baseline pain), the treatments (different salicylates combined with various other potentially active ingredients), and the methods (for example the outcomes reported).

Furthermore for both acute and chronic painful conditions any evidence of efficacy came from the older, smaller studies, while the larger, more recent studies showed no effect.

All these combined led the authors to conclude ‘There is no good evidence that topical salicylate-containing rubefacients give useful pain relief.’

What do you think?

Do you prescribe or use rubefactants for acute or chronic musculoskeletal pain?
Would you now?

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