Gastric microbleeding following single and repeated dosing with naproxen

Background: Adaptation to gastric damage from nonsteroidal anti‐inflammatory drugs (NSAID) has been observed during ongoing dosage in rats and humans. However, this does not always occur, and our previous data suggest that NSAID half‐life may be a determining factor. Aim: To investigate whether adaptation occurs during 1 week of naproxen administration in humans. Subjects: Thirteen healthy volunteers were studied at baseline, and after me or seven daily doses of naproxen 750 mg. Gastric microbleeding was measured 4 h after naproxen in gastric washings collected during a 30‐min period. Serum thromboxane B concentrations were also assayed, as a marker of cyclo‐oxygenase inhibition. Results: Mean blood loss after placebo was 0.60, μL/10 min (95% CI: 0.21–0.98). This rose to 2.15 (0.73–3.57) and 1.75 (0.74–2.76) μL/10 min after one and seven daily doses of naproxen, respectively (P < 0.05 vs. baseline: day 1 vs. 7 not significant). Thromboxane B concentrations were < 10% of control at both day 1 and 7 of dosing. Conclusion: In accord with our findings in rats, adaptation to this moderately long acting NSAID in humans was not apparent. We conclude that any adaptation to naproxen is unlikely to be clinically important.