Oral omeprazole and diclofenac intake is associated with increased faecal calprotectin levels: a randomised open-label clinical trial

Background and aim Nonsteroidal anti-inflammatory drugs and proton pump inhibitors are known to affect the diagnostics of gastrointestinal disorders. The aim of this study was to investigate to what extent omeprazole, diclofenac or co-administration of these affects faecal calprotectin levels and the normalisation interval after cessation. Methods Participants received 20 mg omeprazole daily for 2 weeks in the first sequence, 50 mg oral diclofenac three times daily for 2 weeks in the second and co-administration of these for 2 weeks in the third, with washout periods in between. The first two sequences were randomised to a different order. Faecal calprotectin was measured on days 0, 4, 7, 14, 21, 28 and 35 and thereafter at 7-day intervals until normalisation in each sequence. Results Thirty-two healthy volunteers were included. During drug intake, 39% on diclofenac (median 70.8 µg/g; range 50.2–1080 µg/g), 53% on omeprazole (median 85.3 µg/g; range 51.1–249 µg/g) and 69% on omeprazole + diclofenac (median 101.5 µg/g; range 51.5–532 µg/g) had faecal calprotectin levels above normal. In the diclofenac sequence, faecal calprotectin returned to normal in all participants within 2 weeks of cessation and in the omeprazole and co-administration sequences, within 3 weeks of cessation. No statistical significant difference was found with respect to drug order. Conclusion Short-term intake of omeprazole, diclofenac or co-administration appears to increase faecal calprotectin levels. In patients with increased faecal calprotectin on omeprazole alone or in combination with diclofenac, a repeated faecal calprotectin test is recommended at least 3 weeks after cessation. On diclofenac alone, it is sufficient to repeat the faecal calprotectin test 2 weeks after cessation.