#171 AcetaMINophen for Back and Osteoarthritis Pain: Is the effect in the name?
CLINICAL QUESTION
Is acetaminophen effective for the management of back pain or osteoarthritis?
BOTTOM LINE
Acetaminophen is not efficacious for back pain, and provides no clinically meaningful impact on osteoarthritis. There are many other better interventions for these conditions like: short-term oral NSAIDs for back pain; topical NSAIDs or intra-articular steroids for osteoarthritis; and exercise for both.
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EVIDENCE
- All scales out of 100.
- Back pain:
- One high-quality Randomized Controlled Trial (RCT)1 of 1,652 primary care acute low back patients randomized to acetaminophen regularly 3,990 mg/day versus as needed ≤4,000 mg/day versus placebo x4 weeks.
- No effect on any outcome (time to recovery, pain intensity, disability, function, global symptom change or quality of life) at any time.
- Five systematic reviews2-6 (3-10 RCTs, ≤1,825 patients), mostly acute back pain, acetaminophen.
- Versus placebo: No effect in acute back pain.2-4
- Versus other treatments:
- NSAIDs better (~7.5 points) for pain.5
- Amitriptyline or heat wraps better (~13 points) for pain.6
- Only one small study (29 patients) of chronic pain: Likely inferior to NSAIDs.4
- One high-quality Randomized Controlled Trial (RCT)1 of 1,652 primary care acute low back patients randomized to acetaminophen regularly 3,990 mg/day versus as needed ≤4,000 mg/day versus placebo x4 weeks.
- Osteoarthritis: Eight systematic reviews (4-15 RCTs, ≤5,986 patients).2,7-13
- Versus placebo:
- Pain:2,7,8,11,12 standard mean difference is 0.13-0.18 (likely equals ~3-4 points in 100).
- Does not meet minimal important difference of 0.37 (~9 points).14
- When average change in pain is not meaningful, it is important to consider if any patients could get meaningful change. However, modeling suggests none will with acetaminophen.11
- Pain:2,7,8,11,12 standard mean difference is 0.13-0.18 (likely equals ~3-4 points in 100).
- Versus NSAIDs:
- Pain: NSAIDs improve pain ~6 points versus acetaminophen.10
- Patient assessed global improvement in pain,8 NSAIDs better with Number Needed to Treat (NNT)=6.
- Versus placebo:
- Harms: Acetaminophen increases the risk of elevated liver enzymes (>1.5x normal),2 Number Needed to Harm (NNH)=21.
- Back pain guidelines recommend acetaminophen as 1st-line therapy despite inefficacy.15
- Osteoarthritis guidelines have recommended both for16 and against17 acetaminophen.
- What works best with lowest harms (NNT for pain unless other mentioned):
- Acute back pain: Staying active help return to work (~3 days sooner),18 NSAIDs19 NNT~11, cyclobenzaprine20 NNT~4 (but often adds little after naproxen).
- Chronic back pain: Exercise18 NNT=4-8.
- Osteoarthritis: Topical NSAIDs (hands and knees)21 NNT~5, intra-articular corticosteroid injections22 NNT~4, Exercise23,24 NNT~4-6.
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Not sure I agree with this conclusion. cyclobenzaprine useless.