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Study Findings on Acetaminophen at Odds With Clinical Guidelines

Kate Traynor

Kate TraynorNews Writer
News Center

A recently published report in The BMJ concludes that acetaminophen doesn't do much to relieve low back pain or pain from osteoarthritis of the hip or knee despite being recommended a first-line therapy in some clinical guidelines.

The Australian research team, which included a pharmacist, conducted a meta-analysis to evaluate safety and efficacy data from 13 placebo-controlled randomized clinical trials of acetaminophen in patients with chronic spinal pain or osteoarthritis of the hip or knee.

According to the analysis, acetaminophen was ineffective for the treatment of low back pain and conferred minimal short-term benefits that were not clinically meaningful in patients with osteoarthritis. The report's authors stated that pain management guidelines recommending acetaminophen as a first-line therapy for these conditions should be reevaluated.

"This study does kind of confirm what we see in clinical practice. But I would not throw acetaminophen out the window, either," said Mary Lynn McPherson, professor and vice chair for pharmacy practice and science at the University of Maryland School of Pharmacy in Baltimore.

McPherson specializes in pain management for patients at University of Maryland Primary Care at Heritage Crossing, a primary care practice. She said osteoarthritis, low back pain, and fibromyalgia account for the bulk of the problems her patients face.

"Most patients, by the time they get to me, it's gone beyond acetaminophen," McPherson noted. But she said that if a clinician wants to recommend acetaminophen for low back pain or osteoarthritis, and the patient has no risk factors for liver damage, a 4-g/day dosage is probably needed for a "decent trial" of the drug's effectiveness.

FDA recommends that adults take no more than 4 g of acetaminophen daily, and nonprescription labeling generally recommends no more than 3 g/day for adults.

McPherson said some patients may use the drug as a minor part of a comprehensive regimen that includes other medications and nondrug interventions.

"Overwhelmingly, when you look at most chronic pain—and patients don't want to hear this—really, the most targeted therapy is lifestyle modifications," specifically weight loss and exercise, McPherson said.

But she said it's hard to motivate patients to lose weight and exercise, especially if they are poor, lack transportation, and can't afford to join a gym or visit the local YMCA.

"They're very frustrated," she said of her patients. "It's a Catch-22 if I weigh 300 pounds, and I have osteoarthritis of my knee, and you tell me to go walk, and every time I go walk I feel like there's glass in my knee."

McPherson said she encourages patients to do what they can, including seated exercises and other activities that don't aggravate pain.

Michele Matthews, associate professor at the Massachusetts College of Pharmacy and Health Sciences in Boston, specializes in pain management and addiction. She sees patients about three days a week as an advanced pharmacy practitioner through an arrangement with Brigham and Women's Hospital.

"One of the things I've told my patients is, 'By coming to see me . . . it doesn't mean that you're getting more medication,'" she said.

"Many times, patients start experiencing adverse drug events, and that may be limiting their ability to function more so than the pain itself," Matthews explained. "So I'm oftentimes taking medications away and referring patients to nondrug therapies, including physical rehabilitation or cognitive behavioral therapy."

Her patients, like McPherson's, have often already tried acetaminophen and other nonprescription pain relievers without success and need additional help.

"These patients . . . are very complex, with chronic noncancer pain issues, including low back pain and fibromyalgia and different types of neuropathic pain disorders," Matthews said. "Many of them are not only on many medications but also have multiple comorbidities. So they present many challenges."

Matthews said a multimodal approach is often needed to successfully manage chronic pain—and that approach can include acetaminophen.

"We're trying to emphasize that utilizing multiple medications with different mechanisms of action can actually allow for better pain relief and less incidence of adverse events. So it wouldn't be unreasonable to have a patient on acetaminophen," Matthews said.

But she said expecting acetaminophen alone to improve function and quality of life "is probably not realistic."

She said guidelines are important tools for clinicians, but they quickly become outdated as new data become available. And she emphasized that pain management usually requires patient-specific treatment recommendations.

McPherson noted that guidelines for the treatment of osteoarthritis have recommend acetaminophen as first-line therapy, but that is changing.

The American College of Physicians' 2007 guidelines for the diagnosis and treatment of low back pain recommend acetaminophen or nonsteroidal antiinflammatory drugs as the first-line medications for most patients. But guidelines published last year by the Osteoarthritis Research Society International described acetaminophen as an appropriate intervention only for those patients with knee osteoarthritis who do not have "relevant co-morbidities," such as diabetes and hypertension.

The American Academy of Orthopaedic Surgeons last year rated as "inconclusive" the evidence for and against the use of acetaminophen for the treatment of knee osteoarthritis. The group's guidelines further stated that it is "unreasonable to recommend a treatment that does not show benefit over placebo," as was the case for acetaminophen.

McPherson said it's critical to perform a comprehensive pain assessment to determine the root cause or causes of each patient's pain and the optimal treatment plan.

"When you look at low back pain, for example, so much of it is neuropathic. Often, they should be on an adjuvant drug—gabapentin, pregabalin, an antidepressant, something like that," possibly along with an opioid drug, McPherson said.

Matthews said most patients, when seeking treatment for their pain, are looking for a "magic pill" that will fix things.

"A lot of patients have a really hard time accepting that they have chronic pain, and there's a good chance that it may never completely go away," she said.

[This news story appears in the June 1, 2015, issue of AJHP.]

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