S. Marcuard, Lisa Albernaz, P. Khazanie
Feb 1, 1994
Citations
9
Influential Citations
256
Citations
Quality indicators
Journal
Annals of Internal Medicine
Abstract
Omeprazole, a substituted benzimidazole, is a potent, long-lasting inhibitor of gastric acid secretion [1]; it is now approved in the United States for the treatment of the Zollinger-Ellison syndrome, gastroesophageal reflux disease, and peptic ulcer disease. Omeprazole (Prilosec) is not yet approved for prolonged maintenance therapy of gastroesophageal reflux and peptic ulcer disease as it is in certain European countries. Nevertheless, omeprazole is used in the United States for maintenance therapy of refractory gastroesophageal reflux disease by a substantial number of patients. A decrease (P < 0.05) in serum cyanocobalamin levels develops after 3 to 4 years of omeprazole therapy [2]. However, in patients with the Zollinger-Ellison syndrome receiving omeprazole for up to 4 years, no hematologic abnormalities were noted, but cyanocobalamin levels were not measured [3]. Cyanocobalamin deficiency in humans can result in potentially fatal hematologic and neuropsychiatric abnormalities [4]. Unfortunately, hematologic abnormalities are only seen in severe advanced cyanocobalamin deficiency and, thus, a normal complete blood count can occur in the presence of cyanocobalamin deficiency [5]. Little information is currently available about the potential effect of prolonged oral omeprazole therapy on cyanocobalamin absorption. Cyanocobalamin (vitamin B12) is a water-soluble vitamin derived from certain microorganisms; the vitamin is tightly bound to dietary protein. Hydrochloric acid and pepsin release cyanocobalamin from dietary protein in the stomach where it binds to salivary R proteins [6]. After alteration of R proteins by pancreatic enzymes [7], cyanocobalamin is rapidly transferred to intrinsic factor to form a complex that is resistant to proteolysis [8]. Once the intrinsic factor-cyanocobalamin complex is formed in the upper jejunum, it remains intact until it adheres to specific receptors in the distal ileum. Omeprazole acts by inhibiting the H+/K+ adenosine triphosphatase, a proton pump that seems to be specific to the gastric parietal cells [9-13]. Prolonged omeprazole treatment can result in cyanocobalamin deficiency by three possible mechanisms: 1) In hypo- or achlorhydria, protein-bound cyanocobalamin may not be adequately released from food for transfer to R protein and intrinsic factor; 2) omeprazole may decrease intrinsic factor secretion after long-term therapy even though no effect on intrinsic factor secretion occurred after a single intravenous dose of omeprazole [14], and 3) achlorhydria causes gastric bacterial overgrowth that may accelerate the development of cyanocobalamin deficiency by producing vitamin B12 analogs that compete with absorption and use of the vitamin [15]. We analyzed the effect of omeprazole on cyanocobalamin absorption, because neurologic disorders caused by cyanocobalamin deficiency are often irreversible and can occur in the absence of any hematologic abnormalities [4]. Methods Ten healthy male volunteers with no known gastrointestinal disorders were recruited for this study. All were nonsmokers. Five of the volunteers received 20 mg of omeprazole, and the other five received 40 mg of omeprazole (Prilosec; Merck & Company, Inc., West Point, Pennsylvania) daily for 2 weeks. Participants had modified Schilling tests (protein-bound cyanocobalamin) and gastric analyses, as well as measurements of serum cyanocobalamin, gastrin, and folate levels before and after 2 weeks of omeprazole therapy. The Modified Schilling Test To measure protein-bound cyanocobalamin absorption in the presence of hypo- or achlorhydria, the Schilling test was modified according to the method of King and colleagues [16]. Protein-bound cyanocobalamin doses were made by mixing 1 mL of radiolabeled cobalt-57 cyanocobalamin (10 microcuries; Amersham Corporation, Arlington Heights, Illinois) with 10 mL of sterile water and with 0.2 mL of unlabeled cyanocobalamin (20 g B12) with 45 mL of chicken serum (Grand Island Biological Company, Grand Island, New York). Thus, one test dose contained 1 microcuries of cobalt-57 cyanocobalamin and a total of 2 g of unlabeled cyanocobalamin. After 30 minutes of incubation at room temperature, this mixture was placed in a dialysis membrane with a pore size of 6000 to 8000 molecular weight (PGC Scientifics; Gaithersburg, Maryland). Dialysis was then done for 72 hours at 5 C to remove the unbound cyanocobalamin. The water was changed three times per day. The adequacy of removal of free cyanocobalamin was then tested with a modified Gottlieb charcoal assay by using albumin-coated charcoal [17]. All patients fasted overnight (at least 8 hours) before the Schilling test. Participants received the test solution containing the protein-bound radiolabeled cyanocobalamin followed by an intramuscular injection of 1 mg of cyanocobalamin. Before ingesting the test solution, the participants urinated and started a 24-hour urine collection. The total urine volume and creatinine concentration were measured. The radioactivity in the urine was determined, and results were expressed as the percentage excretion of the ingested cyanocobalamin. The radioactivity of each test dose was measured within 2 hours before administration of the test. Gastric Analysis A nasogastric tube was inserted and advanced until gastric juice could easily be aspirated. The stomach contents were aspirated and, if food or more than 200 mL of liquid was present, the test was canceled. Gastric juice was then collected in 15-minute samples and was placed directly on ice. The pH of each sample was then measured using a glass-tip pH probe (Beckman Instruments, Norcross, Georgia), and the pH was promptly titrated to a pH of 7 to measure total acidity. After the first hour, participants received an injection of 6 g/kg of pentagastrin subcutaneously (Peptavlon; Wyeth-Ayerst Laboratories, Philadelphia, Pennsylvania). Then, four additional 15-minute samples of gastric juice were collected on ice and were titrated to a pH of 7. Serum Analyses Serum cyanocobalamin levels were determined with a protein-binding radioassay using commercially available reagents (Becton Dickinson, Orangeburg, New York). We used a reference range for serum cyanocobalamin of 180 to 960 pg/mL. Gastrin levels in the blood samples were measured using a commercially available radioimmunoassay kit (Becton Dickinson, Orangeburg, New York). Each participant was given a medicine container with 14 doses and was asked to return the container at the end of the study. All studies were carried out using carefully controlled conditions in the gastroenterology laboratory. Informed consent was obtained from all participants, and all investigations were approved by the Policy and Review Committee on Human Research. The Student t-test was used for unpaired and paired samples to determine statistical significance among patient groups. Data are expressed as mean SE. A paired Wilcoxon rank-sum test was also used where applicable. A P value of less than 0.05 was considered significant. Results The mean age of the ten participants was 30.2 2.9 years (range, 22 to 50 years). Their mean height was 1.76 0.02 metres (range, 1.65 to 1.87 metres), and their mean weight was 77.9 6.2 kg (range, 52.2 to 102.1 kg). For the participants receiving 20 mg of omeprazole daily, the mean basal acid output was 2.5 0.8 mEq/h; it decreased to 0.7 0.4 mEq/h after 2 weeks of omeprazole therapy. The five participants who received 40 mg of omeprazole daily had a similar basal acid output of 2.8 1.3 mEq/h that statistically decreased to 0.09 0.08 mEq/h after 2 weeks of therapy. The maximal acid output decreased from 24.7 3.8 mEq/h to 5.8 2.7 mEq/h in the group receiving 20 mg of omeprazole group and from 19.3 5.1 mEq/h to 0.2 0.1 mEq/h in the group receiving 40 mg. Figure 1 shows the suppression of basal acid output and the maximal acid output after omeprazole therapy; achlorhydria occurred in the group receiving 40 mg of omeprazole. Figure 1. Basal acid output and maximal acid output before and after 2 weeks of omeprazole therapy. P Figure 2 shows the results of the modified Schilling test using chicken serum-bound cobalt-57 cyanocobalamin in both groups. One participant in each group had a greater absorption of protein-bound cyanocobalamin than the rest of the participants; we found no explanation for this observation. The mean protein-bound cyanocobalamin absorption at baseline and after 2 weeks of acid suppression with omeprazole is shown in Figure 3. Absorption of protein-bound cyanocobalamin was less than absorption of crystalline cyanocobalamin that is used in the standard Schilling test. As Figure 3 shows, the mean absorption of protein-bound cyanocobalamin at baseline was 3.2% 1.4% and 3.4% 1.3% in the groups receiving 20 mg and 40 mg of omeprazole, respectively. Protein-bound cyanocobalamin absorption decreased (P < 0.05) to 0.9% 0.3% (P = 0.031) and 0.4% 0.1% (P = 0.031) after 2 weeks of 20-mg and 40-mg omeprazole groups, respectively. The median values of protein-bound cyanocobalamin absorption were 2.2% and 2.3% at baseline, which decreased to 0.8% and 0.5% after 20 mg and 40 mg of omeprazole. Figure 2. The modified Schilling test (for protein-bound cyanocobalamin) before and after 2 weeks of omeprazole therapy. Figure 3. Schilling test results before and after 2 weeks of omeprazole therapy. P Serum gastrin levels Figure 4 increased in the group receiving 40 mg of omeprazole from 42 4 ng/L to 105 15 ng/L after 2 weeks (P < 0.01). The serum gastrin levels slightly increased in the group receiving 20 mg of omeprazole from 49 8 to 96 30 ng/L (P = 0.06). Folic acid levels remained unchanged, from a mean of 52 14 ng/mL to 50 12 ng/mL and from 43 13 ng/mL to 45 14 ng/mL in the groups receiving 20 mg and 40 mg of omeprazole, respectively (data not shown). Serum cyanocobalamin levels increased as shown in Figure 5. Cyanocobalamin levels changed from 300 40 pmol/L to 340 50 pmol/L (P > 0.2) in th