AMSTERDAM – Further evidence that acetaminophen has limited benefits in patients with osteoarthritis was presented at the World Congress on Osteoarthritis, with authors of a systematic review calling for reconsideration of guidelines recommending the common analgesic as a first-line option.
“[Acetaminophen] provides minimal short-term benefits for people with hip or knee OA,” said presenting author and rheumatologist Dr. David J. Hunter of the University of Sydney. The treatment effects for both pain relief and for improving physical function were smallest in people with knee OA, he said. “In general, the small effect sizes are unlikely to be clinically relevant,” Dr. Hunter observed.
“These are mean differences across large populations in the clinical trials, and there may be certain individuals with knee or hip osteoarthritis that this may not necessarily apply to,” he conceded during a discussion following his presentation, “but I think from the perspective of the recommendations that come from guidelines, we have got to think about what would be do-able in the general population.”
The findings come shortly after the publication of a large meta-analysis of 74 trials evaluating pain-relieving medications that highlighted the ineffectiveness of acetaminophen for OA pain, particularly when compared against diclofenac and other nonsteroidal anti-inflammatory drugs (Lancet. 2016 Mar 17. doi: 10.1016/S0140-6736(16)30002-2).
Dr. Hunter and coworkers searched clinical trial and medical databases from inception to September 2015 for records relating to acetaminophen use in patients with hip or knee OA. Only placebo-controlled, randomized trials were included, and nine records were found that reported 10 trials involving 3,541 patients. Part of the analysis was published in the BMJ last year (BMJ. 2015;350:h1225. doi: 10.1136/bmj.h1225). The last prior systematic review on the topic was published in 2004 (Ann Rheum Dis. 2004;Aug;63:901–7).
Pain scores were converted to a common 0-100 scale with 0 signifying no pain or disability and 100 the worst possible pain or disability and then expressed as a mean difference between the acetaminophen and placebo groups. Physical function scores were pooled to give a standardized mean difference.
There was high-quality evidence that acetaminophen given at a dose of 3-4 g per day had a significant effect on pain and physical function during a short period of more than 2 weeks to less than 3 months and a more immediate time frame of 2 weeks or less, but it was unlikely to be clinically significant, with a mean difference of just –3.14 for pain and a standardized mean difference of –0.12 to –0.15 for physical function. Differences would need to be at least 9 points for pain and greater than 0.2 for physical function to be clinically significant, Dr. Hunter explained.
Four of the trials considered knee OA only. The mean and standardized mean differences between the acetaminophen and placebo groups in those trials was just –1.09 for pain and –0.06 for physical function.
Similar numbers of patients reported being adherent to their assigned treatment group, with less rescue analgesic use in the acetaminophen-treated patients. Although no differences in adverse events, serious adverse events, or withdrawals because of adverse events were seen, there was a higher risk of liver function test (LFT) abnormalities in the acetaminophen-treated patients. The relative risk for abnormal LFTs was 3.79, but the clinical significance of this is uncertain according to the review’s authors.
“Current guidelines consistently recommend [acetaminophen] as the first line of analgesic medication for this condition,” Dr. Hunter said at the meeting, sponsored by the Osteoarthritis Research Society International. “But these results call for reconsideration of these recommendations.”
The results highlight the importance of using other, nonpharmacologic means to manage pain and physical function, the authors conclude, such as lifestyle changes, weight control, and regular physical exercise.
Dr. Hunter had no disclosures relevant to his comments.