Jane McCredie: Changing evidence

EVIDENCE-based medicine is the mantra of modern-day medical practice.

It underpins the treatment and advice given to patients and is the basis for mainstream medicine’s critique of non-evidence-based alternative therapies.

But what happens when the evidence changes?

A recent large Australian study of paracetamol use for acute lower back pain raises exactly that question.

Clinical guidelines around the world have long recommended paracetamol as the first-line analgesic for acute low-back pain, although there really wasn’t any evidence to support that advice.

The National Prescribing Service’s Back Pain Choices tool for management of low-back pain in primary care, for example, describes paracetamol as “a good first option for pain relief”.

“When taken regularly, paracetamol is as effective as other medications but with fewer side effects”, the tool says.

What’s missing from that advice is the fact that there was never much evidence that any medications were effective against low-back pain.

NHMRC guidelines that were rescinded last year acknowledged as much, calling for placebo-controlled trials of paracetamol, non-steroidal anti-inflammatory drugs and opioids.

We now have that evidence for paracetamol at least, with the large, well designed Australian study showing the drug offered no benefit above placebo in reducing recovery time. It also had no effect on pain, disability, function, global symptom change, sleep or quality of life.

So how did paracetamol become the recommended first-line treatment?

An editorial published in The Lancet alongside the study says: “In the absence of sound clinical evidence, these recommendations favouring paracetamol are based on indirect evidence from other pain specialties, consensus in guideline committees, and the relatively favourable safety profile of paracetamol compared with, for example, non-steroidal anti-inflammatory drugs (NSAIDs).”

Recommendations in guidelines will always be based on differing levels of evidence. And that’s fine as long as they’re transparent about it.

A drug like paracetamol is not a prime target for research: its excellent safety profile means it is seen as a low-risk treatment option and it offers little prospect of financial return for industry.

Which makes this potentially game-changing Australian research all the more welcome.

Interestingly, participants in all arms of the study did better than would normally be expected for patients with acute low-back pain. The median time to recovery was 16 days in the placebo group and 17 in the treatment groups, with nearly 85% of all participants recovering by 12 weeks.

The authors suggest a possible explanation for such good outcomes is that all patients were provided with good-quality advice and reassurance, “a feature that is often absent from usual care”.

It would be interesting to know, as the editorial asks, how patients would have fared if there had been an additional arm to the trial providing advice and reassurance only — without the placebo-triggering addition of either a real or sham pill.

Jane McCredie is a Sydney-based science and medicine writer.