A randomized, double-blind, placebo-controlled 12 week trial of acetaminophen extended release for the treatment of signs and symptoms of osteoarthritis.

Objective: Determine efficacy and safety of acetaminophen extended release (ER) 1300 mg given three times daily compared to placebo for relieving signs and symptoms of hip or knee osteoarthritis.

Methods: Sixty investigators at 58 private, ambulatory, primary care sites in the US enrolled 542 outpatient adults ≥40 years old with moderate to severe idiopathic osteoarthritis pain into a randomized, placebo-controlled, double-blind 12 week clinical trial. Patients were randomly assigned to treatment given three times daily of acetaminophen 1300 mg (n = 267) or placebo (n = 275).

Results: The three primary endpoints measured through week 12 favored acetaminophen ER as follows: least squares (LS) mean change from baseline for WOMAC physical function subscale score was significantly greater for acetaminophen ER than for placebo (P = 0.011); LS mean patient's global assessment of response to therapy was significantly greater for acetaminophen ER than for placebo (P = 0.010); and LS mean change from baseline for WOMAC pain subscale score was marginally greater for acetaminophen ER than for placebo (P = 0.054). LS mean change from baseline for secondary endpoints through week 12 also favored acetaminophen ER compared with placebo: significantly for WOMAC stiffness subscale score (P = 0.004), significantly for WOMAC total index score (P = 0.013), and marginally for Nottingham Health Profile energy subscale score (P = 0.057). The percentage of patients with any adverse event was similar for both treatment groups. Hepatic transaminases exceeded 3 × ULN in seven acetaminophen ER patients and one placebo patient. Elevations were attributed to health conditions in three of seven acetaminophen ER patients; elevations in the remaining four patients returned to or toward normal.

Conclusions: Acetaminophen ER 1300 mg, a nonprescription drug, given three times daily, can provide effective relief of signs and symptoms of osteoarthritis of the hip or knee and was well tolerated. ClinicalTrials.gov registration number: NCT00240799.