Background

Regular paracetamol (acetaminophen) is the recommended first–line analgesic for acute low–back pain; however, no high–quality evidence supports this recommendation. We aimed to assess the efficacy of paracetamol taken regularly or as–needed to improve time to recovery from pain, compared with placebo, in patients with low-back pain.

Methods

We did a multicentre, double–dummy, randomised, placebo controlled trial across 235 primary care centres in Sydney, Australia, from Nov 11, 2009, to March 5, 2013. We randomly allocated patients with acute low-back pain in a 1:1:1 ratio to receive up to 4 weeks of regular doses of paracetamol (three times per day; equivalent to 3990 mg paracetamol per day), as–needed doses of paracetamol (taken when needed for pain relief; maximum 4000 mg paracetamol per day), or placebo. Randomisation was done according to a centralised randomisation schedule prepared by a researcher who was not involved in patient recruitment or data collection. Patients and staff at all sites were masked to treatment allocation. All participants received best–evidence advice and were followed up for 3 months. The primary outcome was time until recovery from low–back pain, with recovery defined as a pain score of 0 or 1 (on a 0–10 pain scale) sustained for 7 consecutive days. All data were analysed by intention to treat. This study is registered with the Australian and New Zealand Clinical Trial Registry, number ACTN 12609000966291.

Findings

550 participants were assigned to the regular group (550 analysed), 549 were assigned to the as–needed group (546 analysed), and 553 were assigned to the placebo group (547 analysed). Median time to recovery was 17 days (95% CI 14–19) in the regular group, 17 days (15–20) in the as–needed group, and 16 days (14–20) in the placebo group (regular vs placebo hazard ratio 0·99, 95% CI 0·87–1·14; as–needed vs placebo 1·05, 0·92–1·19; regular vs as–needed 1·05, 0·92—1·20). We recorded no difference between treatment groups for time to recovery (adjusted p=0·79). Adherence to regular tablets (median tablets consumed per participant per day of maximum 6; 4·0 [IQR 1·6—5·7] in the regular group, 3·9 [1·5—5·6] in the as-needed group, and 4·0 [1·5—5·7] in the placebo group), and number of participants reporting adverse events (99 [18·5%] in the regular group, 99 [18·7%] in the as–needed group, and 98 [18·5%] in the placebo group) were similar between groups.

Interpretation

Our findings suggest that regular or as–needed dosing with paracetamol does not affect recovery time compared with placebo in low–back pain, and question the universal endorsement of paracetamol in this patient group.

Funding

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