Acetaminophen, known in other parts of the world as paracetamol, is often recommended as the first-line treatment for patients experiencing acute low back pain, although its ability to hasten recovery hasn't been well established.

The Paracetamol for Low-Back Pain Study (PACE) was designed to evaluate the efficacy of acetaminophen in recovery from low back pain when used either regularly or as needed. The double-blind, randomized, placebo-controlled trial involved 235 primary care centers in Sydney, Australia, and was conducted from November 2009 until March 2013.

The study subjects were instructed to take regularly scheduled doses and doses as needed for a maximum of four weeks.The 550 patients randomly assigned to the "regular-use" group received a "regular" box of 665-mg modified-release acetaminophen tablets (two tablets to be taken every six to eight hours) and a separate "as-needed" box of identically appearing placebo tablets (one or two tablets taken every four to six hours, for a maximum of eight tablets daily). The 546 patients evaluated in the "as-needed" group received placebo tablets in the regular box and 500-mg immediate-release acetaminophen tablets in their as-needed box. A third group of 547 patients received placebo tablets in both the regular and as-needed boxes.

The patients were asked to document their pain (scored on a scale of 1 to 10) and tablet use in a diary until their recovery or for four weeks (whichever came first). Further follow-up was conducted until week 12. The time to recovery was considered to be the first of seven consecutive days on which the patient's pain score was a 0 to 1 on the scale. Secondary outcomes were pain intensity, sleep quality, quality of life, symptom changes, disability, and function.

The mean age of the patients was 45 years; 53% were men. Recovery occurred by week 12 in 85% of the regular-use group, 83% of the as-needed group, and 84% of the placebo group. The median time to recovery was 17 days in both the regular-use and as-needed groups and 16 days in the placebo group. Further, acetaminophen use had no significant effect on any of the secondary outcomes.

These results suggest that guidelines recommending acetaminophen as the first-line treatment for acute low back pain may need to be rethought and that research should be focused on finding treatments that are effective.-AK

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