This is the message I heard being touted recently by a study
author while listening to the Australian ABC news radio. Could this be? Have we
been prescribing this medication inappropriately for all these years?
As it turns out, the devil is in the details. It all depends
upon which question you are asking.
Enter a large multicentre RCT across 235 primary care centres
in Sydney, Australia. 1652 patients with new low back pain were randomized in a
1:1:1 ratio to receive up to 4 weeks of regular
paracetamol, as-needed paracetamol or
placebo. Patients with suspected serious spinal pathology were excluded
from the study. The methods were quite good and the double-dummy blinding was
quite clever.
Patients were followed up at 1 week and participants
recorded pain scores in to a daily pain and drug diary until recovery or 4
weeks.
The primary outcome
was time to recovery in days. Recovery was defined as the first day of 0 or
1 pain intensity, measured on a 0-10 point scale, maintained for 7 consecutive
days.
Did I read this correctly? The study authors were
trying to determine if paracetamol could cure low back pain? I had no idea that
there were those who thought paracetamol could cure low back pain. I was always
under the impression that it might take the edge off of the pain a little bit
for a brief period of time. But a cure, no.
The authors justified this primary outcome as below.
We chose this outcome on the basis of previous findings of fast
recovery in a cohort receiving regular paracetamol. As such, we postulated that
regular paracetamol would improve recovery by decreasing pain intensity and
allowing people with acute low back pain to remain active and resume normal
movement as soon as possible.
The results showed a median time to recovery of 17 days with
no statistical difference between the groups. So, paracetamol does not cure low back pain. Big surprise.
To be fair, the study did look at secondary outcomes of pain
intensity, disability, function, global rating of symptoms change, sleep
quality and quality of life and found no differences. But one could reasonably
question the validity of the measuring tools. In addition, one should always be
a bit more skeptical when looking at multiple secondary outcomes.
One should also remember that "placebo" is not an inactive treatment arm. To put another way, placebo is not nothing. It can have substantial physiologic and psychological effects in some people especially when it comes to pain. This may have watered down the results of the primary outcome. It would have been interesting if the study had a "nothing" arm.
In the end, this study truly emphasizes the need for
clinicians to be vigilant and emphasizes the value of taking a critical look at
the medical literature. If one was not aware of the study’s primary outcome,
one might be convinced there is no role for paracetamol for low back pain. This
is far from the truth. Nevertheless, I don’t think anyone is deluded that
paracetamol does very much. But at least it is cheap, has a low side effect
profile and might help for a little bit for a brief period of time.
What’s the take home message? Paracetamol is still fine for low back pain and beware what you hear on
the radio.
Covering:
Williams CM, Maher CG, Latimer J, et al. Efficacy of
paracetamol for acute low back pain: a double-blind, randomised controlled
trial. Lancet 24, 2014; [Epub ahead of
print]
Methods
Williams CM, Latimer J, Maher CG, et al. PACE--the first placebo controlled trial
of paracetamol for acute low back pain: design of
a randomised controlled trial. BMC Musculoskelet Disord 2010;11:169
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