Off-label Use of U-500 Regular Insulin with a Tubeless Automated Insulin Delivery System in Type 1 Diabetes and Severe Insulin Resistance: A Case Report

INTRODUCTION: U-500 regular insulin (U-500R) can overcome reservoir-capacity constraints in people with severe insulin resistance, but its delayed and prolonged action is poorly matched to automated insulin delivery (AID) algorithms developed for rapid-acting U-100 insulin analogs. Experience in type 1 diabetes (T1D) is particularly limited. METHODS: We report the off-label transition to Omnipod 5 AID while continuing U-500R in a 46-year-old man with autoimmune T1D, obesity, severe insulin resistance, impaired hypoglycemia awareness (Gold score 6), and frequent isolated overnight work. Before transition, he was receiving approximately 245 units/day of U-500R through an Omnipod DASH patch pump. Initial adaptations included a 6-h active insulin duration, higher overnight glucose targets, semi-quantitative meal announcements, and proactive use of activity mode. RESULTS: Before AID initiation, continuous glucose monitoring showed a mean glucose of 137 mg/dl, glucose management indicator of 6.6%, time in range of 75%, and time below range of 9%. After 12 months, time in range increased to 79.1% and time below range decreased to 5.7%, with 0.4% below 54 mg/dl. Automated mode was active for more than 95% of the time. The patient reported substantially fewer symptomatic hypoglycemic episodes, although occasional hypoglycemia persisted during overnight shifts. CONCLUSIONS: Carefully supervised use of U-500R in an AID system may preserve patch-pump therapy and reduce hypoglycemia exposure in selected people with T1D and very high insulin requirements. This off-label approach requires explicit dose-conversion procedures, conservative individualized settings, close follow-up, and recognition that residual hypoglycemia risk remains.