Situation: A 22-year-old woman with type 1 diabetes mellitus is brought to the emergency department after two days of vomiting, during which she stopped taking her insulin. She weighs 58 kg. Diabetic ketoacidosis (DKA) is diagnosed, and she is admitted to the intensive care unit. Later her DKA has resolved and she is eating. Subcutaneous insulin glargine is ordered to replace the intravenous (IV) insulin infusion. When should the nurse stop the insulin infusion?

IV regular insulin stops acting within minutes, while subcutaneous basal insulin takes time to be absorbed. Giving the basal dose 1–2 hours before stopping the infusion prevents a gap in insulin that could cause rebound hyperglycemia and recurrent DKA.

Core mechanism
When DKA is treated with an intravenous regular insulin infusion, the insulin effect disappears within minutes after the infusion is stopped because regular insulin has a very short half-life. In contrast, subcutaneous insulin glargine is a basal insulin that must be absorbed from the subcutaneous depot before it produces a clinically meaningful glucose-lowering effect. If the IV infusion is stopped before the glargine has begun to work, a gap in insulin coverage occurs, allowing rebound hyperglycemia, ketogenesis, and recurrent DKA. The correct strategy is to overlap the two routes so that the basal insulin reaches effective plasma levels before the continuous IV insulin is discontinued.

Why the overlap timing matters
Subcutaneous glargine has a slow onset because it forms microprecipitates in the subcutaneous tissue after injection, from which insulin is gradually released. Clinically meaningful absorption and onset generally require 1–2 hours. Therefore, the nurse should inject the glargine and continue the IV insulin infusion for an additional 1–2 hours, then stop the infusion. This creates a seamless transition from intravenous to subcutaneous basal coverage.

Key point! The transition is not based solely on the current glucose value. Even if the glucose is below 180 mg/dL (10.0 mmol/L), stopping IV insulin without overlapping basal insulin can still cause rebound hyperglycemia and recurrent ketosis. The glucose threshold reflects DKA resolution, but it does not guarantee that the subcutaneous basal insulin is already effective.

Comparison of transition timing options

Timing of stopping IV insulin	Expected effect	Risk
Thirty minutes before glargine injection	IV insulin effect fades before glargine is even given	Insulin gap, rebound hyperglycemia, recurrent DKA
At the same time as glargine injection	IV insulin stops while glargine is still being absorbed	Partial insulin gap during the first 1–2 hours
One to two hours after glargine injection	Glargine reaches effective levels while IV insulin continues	Seamless transition, lowest risk of rebound DKA
Once glucose is below 180 mg/dL	Stopping based on glucose alone ignores insulin pharmacokinetics	May stop IV insulin before basal coverage is established

Evidence from the literature
The rationale for early basal insulin administration during DKA management is supported by systematic reviews and randomized trials. A meta-analysis of RCTs evaluating early versus late initiation of long-acting insulin in pediatric and adult DKA found that early subcutaneous basal insulin during IV insulin infusion can improve the transition to subcutaneous therapy without increasing hypoglycemia ^[1]. Another systematic review and meta-analysis reported that early basal insulin administration during IV insulin therapy may improve glycemic outcomes in adults with DKA ^[2]. A randomized controlled trial using early insulin degludec with continuous IV insulin infusion also demonstrated that overlapping basal insulin with IV insulin is feasible and safe in DKA management ^[3]. In pediatric type 1 diabetes, early insulin glargine administration has been studied specifically to prevent rebound hyperglycemia and recurrent ketosis after DKA resolution ^[4]. These findings reinforce the principle that basal insulin should be given early enough to overlap with the IV infusion, rather than waiting until the infusion is stopped.

Clinical application for the nurse
When the patient is eating and the order is written to transition from IV insulin to subcutaneous glargine, the nurse should coordinate the timing so that the glargine is injected while the IV infusion is still running. The infusion is then stopped 1–2 hours after the glargine injection. During this overlap period, the nurse continues to monitor capillary glucose and ketones because the patient is still receiving both intravenous and subcutaneous insulin. Watch out! Stopping the IV insulin at the same time as the glargine injection, or earlier, creates a period without adequate insulin action even if the patient is euglycemic at that moment. The risk is not immediate hypoglycemia but delayed rebound hyperglycemia and recurrent DKA.