Paracetamol (Tylenol) ineffective for low-back pain [PACE Study]

1. Paracetamol taken regularly or as needed for low-back pain did not affect recovery time compared with placebo.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Although paracetamol is universally recommended as the first-line analgesic for low-back pain, no high-quality evidence has supported this recommendation. The Paracetamol for Low-Back Pain Study (PACE) assessed the efficacy of paracetamol compared to placebo when taken regularly or as needed for low-back pain. Patients with acute low-back pain were randomized to receive either 4 weeks of paracetamol, paracetamol as needed, or placebo, and followed up for three months. Recovery was defined as a pain score of 0 or 1 out of a 0-10 pain scale for 7 consecutive days.

Regardless of whether paracetamol was taken regularly or as needed, there was no significant difference compared to placebo in minimizing recovery time from low-back pain. Strengths of this study included a large sample size of over 500 participants in each group and the study was adequately powered to detect a difference of 3 days in median time to recovery. Limitations of the study include the fact that participants typically took a lower median dose than the maximum recommended dose, which may have affected the efficacy. The authors suggest that the universal recommendation of paracetamol for use in patients with low-back pain be reconsidered, however, further studies should be conducted before completely dismissing paracetamol as a treatment for low-back pain.

This study was funded by the National Health and Medical Research Council of Australia and GlaxoSmithKline Australia.

Click to read the study, published today in The Lancet

Relevant Reading: An updated overview of clinical guidelines for the management of non-specific low back pain in primary care

In-Depth [randomized controlled trial]: Participants were randomly assigned to one of three groups: paracetamol as needed (maximum 4000 mg/day, n=546), paracetamol at a regular dose (3990 mg/day, n=550) or placebo (n=547). The primary outcome was time in days until recovery from pain as defined by a 0 or 1 pain intensity measured on a 0-10 pain scale for 7 days. Secondary outcomes were pain intensity, disability, function, global rating of symptom change, sleep quality, and quality of life.

By 12 weeks, 466 (85%) participants in the regular group, 452 (83%) in the as-needed group, and 461 (84%) in the placebo group reached recovery. The median time to recovery was 17 days (95% Confidence Interval [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 [HR] 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). Time to recovery did not significantly differ between groups (p = 0.55), even when calculating for best-case and worst-case recovery. Participants in all groups reported decreased treatment adherence, decreasing from 3500 mg/day in week 1 to 2800 mg/day in week 2. The median number of tablets taken daily was 4.0 (Interquartile range [IQR] 1.5-5.7, 2660 mg/day) in the regular group, 1.9 (IQR 1.0-4.0, 1000 mg/day) in the as-needed group in week 1 with 1.0 (0.4-2.7, 500 mg/day) daily overall, and 4.0 (IQR 1.5-5.7) daily in the placebo group. Adverse events were similar in all groups, with 99 (18.5%) reported in the regular group, 99 (18.7%) in the as-needed group, and 98 (18.5%) in the placebo group.

Image: PD 

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