Background: Shortly after Roux-en-Y gastric bypass (RYGB) surgery, insulin requirements decrease rapidly and insulin dependent type 2 diabetes mellitus (T2DMi) patients have increased risk of hypoglycemia. Guidelines on insulin management directly after RYGB surgery does not exist. Therefore, a standardized insulin reduction protocol was developed and evaluated on safety and efficacy.

Methods: The protocol aimed to maintain blood glucose level (BGL) between 5 and 15 mmol/l the first ten postoperative days. At the day of surgery (D0), insulin dose was reduced by 75% and long acting nighttime insulin was replaced by glimepiride. After discharge (2^nd postoperative day, D2) BGL was managed by phone, until final consultation 3 months after surgery. All BGL and adjustments in antidiabetics in this period were evaluated.

Results: 151 patients were included. Preoperative insulin dose was 130±80 IU/day, and decreased to 37±1.9 IU/day at D0. From D0-D2, 3% of all BGL measurements were <5 mmol/l and 3 patients had a hypoglycemic event (BGL 3.1-3.5 mmol/l). BGL>15 mmol/l mainly occurred on D0 (13% of the measurements), and decreased to 3% from D1-D2.

From D3-D10, 7% of all BGL was <5 mmol/l and 8 patients had a hypoglycemic event (BGL 2.3-3.5 mmol/l). BGL was >15 mmol/l in 2% of the measurements. None of the patients needed help. Antidiabetics were adjusted based on BGL day curves. At final consultation, insulin was discontinued in 82% of the patients and in 19% of the patients all antidiabetics were discontinued. In patients not discontinued insulin, the dose was decreased to 30±4.2 IU/day. Fasting glucose and HbA1c decreased from 11.3±0.29 to 8.4±0.24 mmol/l and from 70±1.4 to 54±1.0 mmol/mol (P<0.01), respectively. One patient had dysregulated BGL and hospital admission was required.

Conclusion: An immediate 75% reduction of insulin dose with rapid response monitoring is safe and effective in the large majority of patients with T2DMi undergoing RYGB surgery. Hypo- and hyperglycemia were prevented and antidiabetics were further reduced or discontinued rapidly.