Effect of short- and long-term treatment with omeprazole on the absorption and serum levels of cobalamin

Aims: To evaluate absorption of protein-bound and unbound cyanocobalamin before and during treatment with omeprazole, and cobalamin levels in patients on long-term treatment with omeprazole. Methods: In eight former duodenal ulcer patients absorption of unbound and protein-bound cobalamin was determined by measuring 24-h urinary excretion of unbound ⁵⁸Co-cyanocobalamin or protein-bound ⁵⁷Co-cyanocobalamin during a modified Schilling test. Tests were performed before and during treatment with 20 mg and 40 mg omeprazole daily for 9 days. Serum cobalamin levels were assessed in 25 patients with gastro-oesophageal reflux disease (GERD) before and during long-term maintenance therapy with omeprazole. Mean treatment duration was 56 months (range 36-81 months). Results: Urinary excretion of unbound cobalamin was unchanged with both dosages of omeprazole. Excretion of ⁵⁷Co-cyanocobalamin, however, decreased significantly during treatment with both 20 mg omeprazole (mean ± S.E.M.: 1.31 ± 0.20 vs. 0.54 ± 0.17%; P < 0.02) and 40 mg omeprazole (1.25 ± 0.26 vs. 0.29 ± 0.06%; P < 0.02). Mean serum cobalamin levels (± S.E.M.) before and during therapy with omeprazole in GERD patients were 298 ± 27 and 261 ± 16 pg/mL (normal range 180-900 pg/mL), respectively (P = N.S.). Conclusions: Absorption of protein-bound, but not unbound, cyanocobalamin is decreased when measured by a modified Schilling test during treatment with omeprazole. However, no change in serum cobalamin levels was observed in patients with GERD after treatment with omeprazole for up to 7 years.