Acetaminophen for Chronic Pain: A Systematic Review on Efficacy

Abstract

Acetaminophen (paracetamol) is the most commonly used analgesic worldwide and recommended as first-line treatment in all pain conditions by WHO. We performed a systematic literature review to evaluate the efficacy of acetaminophen when used for chronic pain conditions. Applying three broad search strategies for acetaminophen use in chronic pain in both Embase and PubMed, 1551 hits were obtained. After cross-reference searches of both trials and 38 reviews, seven studies comparing acetaminophen in continuous dosing regimens of more than 2 weeks with placebo were included. The review was conducted according to the PRISMA guidelines. All studies were conducted in patients with hip-or knee osteoarthritis and six of seven studies had observation periods of less than 3 months. All included studies showed no or little efficacy with dubious clinical relevance. In conclusion, there is little evidence to support the efficacy of acetaminophen treatment in patients with chronic pain conditions. Assessment of continuous efficacy in the many patients using acetaminophen worldwide is recommended.Acetaminophen (paracetamol) has been widely endorsed as a first-line analgesic and is currently the most commonly used analgesic worldwide (1). As an example, 9.6% of all Danes obtained acetaminophen via prescription in 2013, with the prevalence rising to an astonishing 23% among 65-to 79-yearolds and 45% among octogenarians (2). The recommendation of using acetaminophen has been generalized by the World Health Organization (WHO), suggesting acetaminophen as the first step in any pharmacological pain treatment (3). Similarly, acetaminophen is recommended as first-line treatment in many chronic pain conditions such as osteoarthritis (4) and for geriatric patients in general (5). The wide endorsement of acetaminophen is primarily attributable to a favourable safety profile compared with other treatment options (6), and the notion that acetaminophen has an efficacy comparable with non-steroid anti-inflammatory drugs (NSAIDs) -the latter primarily based on a highly cited study from 1991 by Bradley et al. (7).While a solid evidence base exists for the use of acetaminophen in acute pain states such as dental and post-operative pain (8), post-partum pain (9) and migraine (10), the evidence supporting its use in chronic pain conditions is less obvious. In a pivotal and often cited study from 1983, Amadio and Cummings showed that acetaminophen was superior to placebo in patients with osteoarthritis (OA) (11). While this cross-over study was only based on 25 patients, it has served as a basis for subsequent investigations, and as such, later studies often compare acetaminophen directly to NSAIDs (12) or COX2 inhibitors (12), without including an arm receiving placebo.Considering the widespread and often long-term use of acetaminophen, it is of major public health importance to ensure that this use is founded on solid evidence regarding efficacy. To this end, we conducted a systematic literature review to assess the efficacy of acetamin...

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