How do you convert an insulin infusion to a divided dose of short-acting insulin (e.g. Novolog (insulin aspart) or Humalog (insulin lispro)) and long-acting insulin (e.g. Lantus (insulin glargine) or Levemir (insulin detemir))?

Converting Insulin Infusion to Divided Subcutaneous Doses

To convert from IV insulin infusion to subcutaneous insulin, calculate the total 24-hour IV insulin dose, then give 50% as long-acting basal insulin (glargine or detemir) once daily in the evening, and divide the remaining 50% equally among three meals as rapid-acting insulin (aspart, lispro, or glulisine). 1

Step-by-Step Conversion Algorithm

Step 1: Calculate Total Daily Insulin Requirement

• Determine the total amount of IV insulin infused over the past 24 hours 1
• Use the infusion rate from the final 6-8 hours of the IV infusion for the most accurate calculation 2
• Example: If infusing 2 units/hour × 24 hours = 48 units total daily dose

Step 2: Divide Into Basal and Bolus Components

Basal insulin (long-acting):

• Give 50% of the 24-hour IV insulin total as basal insulin (glargine/Lantus or detemir/Levemir) 1
• Administer as a single dose in the evening 1
• Example: 48 units ÷ 2 = 24 units of glargine once daily

Bolus insulin (rapid-acting):

• Give the remaining 50% of the 24-hour IV insulin total, divided by 3, as rapid-acting insulin before each meal 1
• Use aspart (Novolog), lispro (Humalog), or glulisine before breakfast, lunch, and dinner 1
• Example: 48 units ÷ 2 = 24 units ÷ 3 = 8 units before each meal

Step 3: Timing of Transition

• Administer the first dose of basal insulin 2 hours before discontinuing the IV insulin infusion 2
• Continue IV insulin until the basal insulin has time to begin working 2
• Give the first rapid-acting insulin dose with the next meal after transition 1

Step 4: Adjust for Nutritional Status

• If the patient has insufficient caloric intake or is NPO, reduce both basal and bolus doses by 50% 1
• Resume full doses when normal oral intake resumes 1

Alternative Dosing Strategies Based on Evidence

Higher Conversion Ratios

Research suggests that using 80% of the total daily IV insulin requirement as basal insulin may achieve better glycemic control in the first 24 hours compared to 40-60% conversion 2. However, the guideline-recommended 50% split remains the standard approach 1.

Weight-Based Approach

• An alternative is 0.5 units/kg of basal insulin for patients transitioning from IV insulin 3
• This approach may result in higher basal doses but has shown similar safety profiles 3
• The percentage-based method (50% of TDI) remains more widely validated 1, 2

Monitoring and Titration

Initial Monitoring

• Check capillary blood glucose before each meal and at bedtime 1, 2
• Monitor for hypoglycemia, especially in the first 24-48 hours 2, 3

Dose Adjustments

• For fasting hyperglycemia: Increase basal insulin by 2 units every 3 days until fasting glucose reaches target 1
• For post-prandial hyperglycemia: Increase the corresponding meal's rapid-acting insulin by 1-2 units or 10-15% 1
• For hypoglycemia: Reduce the corresponding insulin dose by 10-20% if no clear precipitating cause is identified 1, 4

Common Pitfalls and How to Avoid Them

Pitfall 1: Using Unstable Infusion Rates

• Avoid calculating from periods of rapidly changing insulin requirements 2
• Use the most recent 6-8 hours of stable infusion rates for calculation 2

Pitfall 2: Inadequate Overlap Time

• Failure to overlap IV and subcutaneous insulin leads to hyperglycemic gaps 2
• Always give basal insulin 2 hours before stopping IV insulin 2

Pitfall 3: Not Adjusting for NPO Status

• Continuing full doses in NPO patients causes severe hypoglycemia 1
• Reduce both basal and bolus by 50% when caloric intake is insufficient 1

Pitfall 4: Overlooking Insulin Resistance

• Patients with high BMI or on medications like steroids may need higher doses 4, 5
• Consider starting at 0.3 units/kg for basal insulin in insulin-resistant patients 5

Special Populations

Type 1 Diabetes

• Always maintain basal insulin coverage to prevent diabetic ketoacidosis 1, 4
• Resume the patient's usual basal-bolus regimen at hospital doses 1

Type 2 Diabetes on Oral Agents

• Continue metformin if renal function permits (eGFR >30 mL/min for most agents, >60 mL/min for metformin) 1
• Consider gradually reducing rapid-acting insulin as oral agents resume effect 1

Steroid-Induced Hyperglycemia

• Use NPH insulin in the morning rather than long-acting analogs to match steroid pharmacokinetics 4
• Start at 0.1-0.2 units/kg daily, with higher doses (0.3 units/kg) for insulin-resistant patients 4, 5