Gastrointestinal blood loss during treatment with naproxen for rheumatoid arthritis.

In 9 patients with active rheumatoid arthritis we studied gastrointestinal blood loss during well tolerated therapy with the non-steroidal anti-inflammatory drug naproxen, 500 mg twice daily. The mean gastrointestinal blood loss, assessed with reinfused autologous 51Cr-labelled erythrocytes, was 1.4 +/- 0.6 ml/day (mean +/- SD) and did not exceed the upper normal level. No relationship was observed between individual gastrointestinal blood loss and serum concentrations of protein-unbound or of total naproxen, or of the duration of drug treatment, or of the degree of disease activity of rheumatoid arthritis. Two subjects developed peptic ulcer disease after the study, from which they had a blood loss of 0.9 and 1.9 ml/day, respectively.