Back Pain and Paracetamol

Back Pain and Paracetamol

Medicine in the News

There has been a lot of news and talk about a recent article that 'shows': "Paracetamol does not help lower back pain" - The Guardian 23/7/14
"Paracetamol may not be effective for back pain" - ABC 24/7/14
"Paracetamol doesn't work for back pain" - SMH 24/7/14
So what does the study show and what does other evidence show?

By Paracetamol_acetaminophen_500_mg_pills.jpg: Michelle Tribe from Ottawa, Canada derivative work: Anrie (Paracetamol_acetaminophen_500_mg_pills.jpg) [CC-BY-3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

The study

On the 24/7/14 The Lancet  published the article "Efficacy of paracetamol for acute low-back pain: a double-blind, randomised controlled trial"  and called themselves the PACE study (Paracetamol for Low-Back Pain Study).  

The study was a RCT which looked at paracetamol in the treatment of acute lower back pain without neurological symptoms.
The study randomised 1652 patients to one of three groups:
1. regular paracetamol 665mg x2 TDS (3990mg daily)
2. PRN paracetamol 500mg x 2 QID PRN (4000mg daily max)
3. Placebo

The study was run from multiple GP practices through Sydney Australia from 2009 to 2012. Follow up was conducted over three months from onset of treatment. It had good patient retention.  It was well randomised.

It had a neat way of blinding the study which I thought would be good to explain.  It gave each patient a box, containing regular tablets and PRN tablets.  Each groups tablets are below:

• In the regular paracetamol group 
• 2 x 665mg paracetamol TDS
• 2 x placebo PRN QID
• In the PRN paracetamol group
• 2 x placebo TDS
• 2 x 500mg paracetamol PRN QID
• In the Placebo group
• 2 x placebo TDS
• 2 x placebo PRN QID

 Patients were told to take both the regular and PRN tablets regardless of their group.

The Results

There was no difference between all three groups.

That's right, no difference.

'Maybe they didn't measure the right stuff?'

One thing that the news did report was the 'primary outcome' of the study: time till pain free.  Before reading the article I questioned whether this was a good outcome.  Let's face it, paracetamol is not a disease modifying agent.  It wouldn't make sense for paracetamol to stop a nociceptive stimulus .  I would only expect the amount of pain to be less for the duration of the study and maybe not for the time to pain free to be effected.  So I wondered to myself as I read and heard the news if it was simply a case of measuring the wrong thing.

But:
There was no difference in pain score either.

The main goal of the study was to see time to when the pain stopped, but it also looked at pain levels, amount of other therapy used, sleep, work, disability and range of other factors.

In all three groups, regular paracetamol, PRN paracetamol, and regular placebo with PRN placebo there was no significant finding in any of the measured outcomes.  One outcome that I loved reading was the question - 'which of your tablets were real and which were placebo.

  Patient belief \ Treatment group     regular                 PRN                 placebo   
Neither contained paracetamol      113/498 (23%)     137/494 (28%)     156/505 (31%)

Regular contained paracetamol       261/498 (52%)     224/494 (45%)     237/505 (47%)


As-needed contained paracetamol  124/498 (25%)      133/494 (27%)     112/505 (22%)

As you can see it seemed pretty random if patients were able to correctly identify if they had placebo in both, regular or PRN paracetamol.  I thought this was a funny thing to measure but it does show that the patients were unaware of which tablet was active or placebo and that a lot of patients must have falsely attributed a positive or negative effect to a placebo tablet.

Interpretation

This study is pretty convincing that paracetamol is not an effective treatment for simple acute lower back pain.

The study mentions one of its own limits is that a lot of the patients had pretty poor compliance with treatment.  In the first week there was good compliance, but towards the end of the study (like towards week 12) patients were on average taking around 1 tablet a day.  I think that this is a really interesting limit to talk about because it says that 'theoretically there might be an effect of paracetamol if people take it regularly for a long time but even in a well controlled study where patients were reinforced to take the paracetamol most of the didn't.'  I guess the challenge that this raises is that from the study we can't say that strict regular paracetamol will or will not help.  But what we can say from the study is that if we recommend regular paracetamol or if we don't it probably won't have an effect.  

The other main thing to note about interpretation of the study is that this study only looks at one area.  This study doesn't show that paracetamol is not helpful across the board - other studies have shown it to be effective at treat pain in other settings.  Rather this study shows only that it is not very useful in acute lower back pain.

TLDR:

A well run study that looked at paracetamol vs placebo in acute lower back pain found no difference.

So the questions for us now are:

Should we use it anyway?

Did the study miss the effect? 

Is paracetamol just a placebo anyway?

Are you going to read the study?

Good luck and Have Fun!

Laurence out