Suicide via Intentional Insulin Overdose Through First Commercial Hybrid Closed-Loop

The Medtronic MiniMed 670G is the Food and Drug Administration approved hybrid closed-loop (HCL) system automatically modulating insulin delivery (Auto Mode) every five minutes based on continuous glucose monitor (CGM) values and reducing hypoglycemia in patients with type 1 diabetes (T1D).^1,2 We report a first case of suicide by taking repeated high doses of insulin through the Medtronic 670G.

A 51-year-old male with 20 years of T1D had HbA1c of 7.5% to 8% using the Medtronic 670G for 18 months (Figure 1(a)). He had no diabetic microvascular complications and took a statin for hyperlipidemia. He was using citalopram for depression for one year which was tapered off three months prior to the event. On the day of his death, at about 8:30 am, he disabled HCL Auto Mode and dosed about 180 U of insulin (twice his total daily insulin requirement) within 45 to 60 minutes. The CGM glucose started dropping rapidly between 8:45 and 9:45 am and he may have become unconscious by around 10:45 am (Figure 1(b)). Despite his CGM glucose being undetectable, he continued receiving basal insulin at the preset rate of 1.5 U/h. He was found unresponsive at 7:00 pm, resuscitated, and kept in intensive care for two days until he was declared brain dead and life support was withdrawn.

Figure 1.

(a) Typical Medtronic 670G glucose profile when in Auto Mode with insulin delivery statistics. The left panel shows three characteristic days of the patient’s usual glucose profile (black lines are sensor glucose, small pink lines are automated insulin delivery every five minutes based on sensor glucose, and blue lines are meal related boluses taken by the patient) and the right panel shows sensor and insulin delivery statistics over 15 days from 3 months prior to his suicide. (b) Profile of insulin overdose event. The sensor glucose over time and insulin boluses on the day of suicide. The patient delivered a total of 180 U over 60 minutes between 8:45 and 9:45 am (blue lines). Based on his sensor glucose tracing (black line), we estimate that he may have become unconscious by around 10:45 am when his sensor glucose was undetectable. Insulin pump was delivering basal insulin (pink line) at rate of ~1.5 U/h despite his sensor glucose being undetectable.

This case illustrates the psychological challenges in patients with T1D and the limitations in the most advanced technologies. While recommendations exist to address suicidal thoughts in patients on insulin therapy, it is impossible to remove access to insulin from adults with T1D.^3,4 This patient disabled HCL Auto Mode before taking multiple boluses; however, we believe enabling Auto Mode may not have changed the outcome since the Medtronic 670G exits Auto Mode for sustained hypoglycemia and minimum basal insulin delivery.⁴ This case highlights the need for future insulin delivery systems to be made even safer. In addition to the maximum bolus delivery feature, future systems can make technology safer by (a) not allowing more than a certain amount of bolus insulin in a given time period (eg, no more than 40% of the usual total daily dose over two hours), (b) making predictive low glucose suspend a standard and default feature, (c) allowing suspension of insulin delivery for longer times (current limit of insulin suspension is two hours) until CGM glucose is above 70 mg/dL, and (d) automating share, texting, or calling features to family members or emergency services if CGM glucose is below 54 mg/dL for more than certain period. Adding these safety features may not fully prevent harm in cases of suicide, however, it would increase the hindrance toward successful self-harm and could potentially deter individuals long enough to reconsider their decision or give companions and/or caregivers more time to recognize and address the situation.⁵