Effect of a topical diclofenac solution for relieving symptoms of primary osteoarthritis of the knee: a randomized controlled trial

Background: Treatment of osteoarthritis with oral NSAID therapy provides pain relief but carries a substantial risk of adverse effects. Topical NSAID therapy offers an alternative to oral treatment, with the potential for a reduced risk of side effects. The objective of this trial was to assess the safety and efficacy of a topical diclofenac solution in relieving the symptoms of primary osteoarthritis of the knee. Methods: We identified 248 men and women from southern Ontario with primary osteoarthritis of the knee and at least moderate pain. The patients were randomly assigned to apply 1 of 3 solutions to their painful knee for 4 weeks: a topical diclofenac solution (1.5% wt/wt diclofenac sodium in a carrier containing dimethyl sulfoxide [DMSO]); a vehicle-control solution (the carrier containing DMSO but no diclofenac); and a placebo solution (a modified carrier with a token amount of DMSO for blinding purposes but no diclofenac). The primary efficacy end point was pain relief, measured by the Western Ontario and McMaster Universities (WOMAC) LK3.0 Osteoarthritis Index pain subscale. Secondary end points were improved physical function and reduced stiffness (measured by the WOMAC subscales), reduced pain on walking and patient global assessment (PGA). Safety was evaluated with clinical and laboratory assessments. Results: In the intent-to-treat group the mean change (and 95% confidence interval [CI]) in pain score from baseline to final assessment was significantly greater for the patients who applied the topical diclofenac solution (-3.9 [-4.8 to -2.9]) than for those who applied the vehicle-control solution (-2.5 [-3.3 to -1.7]; p = 0.023) or the placebo solution (-2.5 [-3.3 to -1.7]; p = 0.016). For the secondary variables the topical diclofenac solution also revealed superiority to the vehicle-control and placebo solutions, leading to mean changes (and 95% CIs) of -11.6 (-14.7 to -8.4; p = 0.002 and 0.014, respectively) in physical function, -1.5 (-1.9 to -1.1; p = 0.015 and 0.002, respectively) in stiffness and -0.8 (-1.1 to -0.6; p = 0.003 and 0.015, respectively) in pain on walking. The PGA scores were significantly better for the patients who applied the topical diclofenac solution than for those who applied the other 2 solutions (p = 0.039 and 0.025, respectively). The topical diclofenac solution caused some skin irritation, mostly minor local skin dryness, in 30 (36%) of the 84 patients, but this led to discontinuation of treatment in only 5 (6%) of the cases. The incidence of gastrointestinal events did not differ between the treatment groups. No serious gastrointestinal or renal adverse events were reported or detected by means of laboratory testing. Interpretation: This topical diclofenac solution can provide safe, site-specific treatment for osteoarthritic pain, with only minor local skin irritation and minimal systemic side effects.