Omeprazole (e.g. Prilosec) is a potent protein-pump inhibitor (PPI) antacid that is more effective than histamine-2 receptor antagonists antacids (e.g. famotidine) in raising intragastric pH in cats. For this reason, omeprazole is often the first choice acid suppressant prescribed to cats with diseases suspected to result in excessive gastric acidity, ulcerative esophagitis, gastritis or gastrointestinal (GI) bleeding.

In humans, prolonged omeprazole use can result in severe adverse effects, including an increased risk of community-acquired pneumonia and Clostridium difficile infections, undesired drug interactions, cobalamin (vitamin B12) deficiency, and disruption of calcium and magnesium balance with subsequent development of osteoporosis and pathologic fractures. In addition, a phenomenon known as rebound acid hypersecretion (RAH) has been shown to occur after abrupt cessation of omeprazole administration with prolonged treatment.

Despite evidence that prolonged PPI administration is associated with adverse effects in humans, no studies have investigated the potential adverse effects for chronic PPI use in cats. Therefore, researchers from the University of Tennessee College of Veterinary Medicine and collaborators evaluated the effect of prolonged oral omeprazole administration on serum calcium, magnesium, cobalamin, and gastrin concentrations and on bone mineral density and content in cats. An additional smaller subset of cats was evaluated for evidence of RAH following abrupt cessation of omeprazole therapy.

In this study, six healthy older adult cats (≥7 years of age), in a before and after design, received placebo followed by omeprazole for 60 days each. Serum calcium, magnesium, cobalamin, and gastrin concentrations were measured on days 0, 30, and 60. Bone density and content were evaluated on days 0 and 60 of each intervention. On day 60 of omeprazole administration, pH capsules were attached within the stomachs of 2 cats and continuous intragastric pH monitoring was performed in order to evaluate the effects of abrupt withdrawal of omeprazole.

In conclusion, no cats had a statistically significant decrease in serum concentrations of magnesium, calcium, cobalamin, methylmalonic acid (elevated with cobalamin deficiency), bone mineral content, and bone mineral density after 30 or 60 days of omeprazole treatment. Although the sample size was small, results of this pilot study suggest that oral omeprazole is relatively safe for healthy cats at courses ≤8 weeks in duration.  In addition, gastric hyperacidity was seen in both cats in which intragastric pH monitoring was performed following abrupt cessation of omeprazole. (GO)