Rabson-Mendenhall syndrome is a rare genetic disorder resulting from mutations in the insulin receptor and is associated with high degrees of insulin resistance. These patients are prone to complications secondary to their hyperglycemia including diabetic ketoacidosis (DKA). We report the case of a 19-year-old male with Rabson-Mendenhall syndrome presenting with DKA who required doses of up to 500 U/h (10.6 U/kg/h) of insulin. The patient’s insulin infusion was originally compounded with U-100 regular insulin, although to minimize volume, the product was compounded with U-500 insulin. The DKA eventually resolved requiring infusion rates ranging from 400 to 500 U/h. Although numerous opportunities for medication errors exist with the use of U-500 insulin, this case outlines the safe use of concentrated intravenous insulin when clinically indicated for patients requiring extremely high doses of insulin to control blood glucose.