What is the evidence for acetaminophen in treating osteoarthritis of the knee?
AMSTAR Rating
Summary
Patient Population:
Adult participants with OA. The reported mean age of participants was 62.2 years. 69% of participants were female.
Intervention:
Dosage of acetaminophen varied, however in 12 trials 1000mg oral acetaminophen was used four times a day.
Comparison:
There were 15 RCTs identified for inclusion (n=5986 participants). In 7 RCTs acetaminophen was compared to placebo. 10 trials included the comparison of acetaminophen to treatment with an NSAID.
Outcome:
- Pain: acetaminophen vs. placebo – significant difference in favour of acetaminophen (SMD=-0.13, 95% CI -0.22,-0.04; NNT=16).
- NSAIDs: Acetaminophen was less effective than NSAIDs in terms of pain reduction, WOMAC pain, stiffness, function, global assessments and functional status. For overall pain, treatment with NSAIDs appeared superior to acetaminophen; effect sizes ranged from SMD-0.25 (95% CI =95% CI -0.33, -0.17) to -0.31 (95% CI -0.40, -0.21).
- Safety: Patients taking NSAIDs, compared to those taking acetaminophen, were more likely to experience an adverse GI event (RR 1.47, (95% CI 1.08 to 2.00).
Guideline Recommendations
Outcomes Assessed
- Benefit
- Harm
- Inconclusive
Acetaminophen vs. Placebo
Pain
Acetaminophen vs. NSAIDs
Pain
Stiffness
Function
Safety
Relevant Clinical Info
The NNT to achieve an improvement in pain ranged from 4 to 16. No significant difference was found overall between the safety of acetaminophen and NSAIDs, although patients taking traditional NSAIDS were more likely to experience an adverse GI event (RR 1.47, (95% CI 1.08 to 2.00). 19% of patients in the traditional NSAID group versus 13% in the acetaminophen group experienced an adverse GI event.
