Insulin autoimmune syndrome induced by omeprazole in an Asian Male with HLA-DRB1*0406 Subtype: A case report

Insulin autoimmune syndrome (IAS) is characterized by hyperinsulinemic hypoglycemia and elevated anti-insulin antibodies. While thiol-containing drugs commonly induce IAS, cases induced by proton pump inhibitors are rare. We report a case of IAS induced by omeprazole in a 27-year-old Chinese man with the HLA-DRB1*0406 subtype. This patient presented with Whipple’s triad after taking omeprazole without concurrent insulin use. The mixed-meal tolerance test (MMTT) and insulin-C-peptide release tests revealed a rapid surge in insulin levels within one hour, with a non-significant increase in C-peptide and a significant rise in insulin after precipitation. Further examination revealed high-titer positive insulin autoantibodies, leading to a diagnosis of insulin autoimmune syndrome (IAS). Symptoms resolved upon discontinuation of omeprazole and adherence to dietary recommendations, with insulin autoantibody levels decreasing after a 6-month follow-up. This case highlights omeprazole’s potential to induce IAS, underscoring the need for vigilance due to widespread use of proton pump inhibitor.