Additive effect of combined naproxen and paracetamol in rheumatoid arthritis.

The clinical effect and plasma naproxen levels were studied in 20 patients with RA receiving three doses of naproxen and two naproxen doses combined with paracetamol (acetaminophen) in a randomized, double-blind, comparison in five 2-wk treatment periods. A significant dose-concentration effect relationship was found for the three naproxen doses (500, 1000 and 1500 mg daily). The following variables were measured: global clinical effect, joint index, morning stiffness, activity of daily living (ADL), pain during movement and at rest. The naproxen dose-concentration effect relationship curve was moved to the left by the addition of 4 g paracetamol daily. No major side effects were observed, but complaints concerning the gastrointestinal tract were fewer on lower naproxen doses and these were not increased by concomitant paracetamol treatment. The results show that the clinical effect of naproxen in RA may be significantly increased by concomitant paracetamol administration.