How to calculate insulin dose in a patient?

How to Calculate Insulin Dose in a Patient

For insulin-naive patients with type 2 diabetes, start with 10 units per day OR 0.1-0.2 units/kg per day of basal insulin, then titrate by increasing 2 units every 3 days to reach fasting plasma glucose goal without hypoglycemia. 1

Initial Basal Insulin Dosing

Starting Dose Calculation

• Begin with 10 units per day as a flat dose OR calculate 0.1-0.2 units/kg per day for insulin-naive patients or those on low insulin doses 1
• For patients with type 1 diabetes who are metabolically stable, use 0.5 units/kg/day as the typical initial total daily dose 2
• Higher doses of 0.5-1.0 units/kg/day are needed during puberty, pregnancy, and medical illness 2
• Consider lower doses (0.3-0.5 units/kg) for patients at higher risk of hypoglycemia, including those over 65 years, with renal failure, or poor oral intake 2

Titration Algorithm

Use this evidence-based approach for basal insulin titration: 1

• Set a fasting plasma glucose (FPG) goal based on individualized glycemic targets
• Increase the dose by 2 units every 3 days to reach FPG goal without hypoglycemia 1
• For hypoglycemia: determine the cause; if no clear reason exists, lower the dose by 10-20% 1
• Assess adequacy of insulin dose at every visit 1

Common pitfall: Avoid using sliding scale insulin alone in patients with established diabetes, as this approach is associated with clinically significant hyperglycemia and should be discouraged 1

Advancing to Basal-Bolus Regimens

Total Daily Dose Distribution

When A1C remains above goal on basal insulin alone, transition to a basal-bolus regimen: 1, 2

• Allocate approximately 50% of total daily dose (TDD) to basal insulin 2
• Distribute the remaining 50% as bolus (prandial) insulin before meals 2

Initiating Prandial Insulin

Start with one dose at the largest meal or meal with greatest postprandial glucose excursion: 1

• Begin with 4 units per day OR 10% of basal insulin dose 1
• Increase dose by 1-2 units or 10-15% based on postprandial glucose readings 1
• If A1C <8% when adding prandial insulin, consider lowering basal dose by 4 units per day or 10% 1

Stepwise Intensification

If glycemic control remains inadequate, proceed systematically: 1

• Add prandial insulin to additional meals sequentially
• Consider twice-daily premixed insulin or self-mixed/split insulin plans 1
• Progress to full basal-bolus regimen (basal insulin plus prandial insulin with each meal) 1

Special Circumstances

Hospital Inpatient Dosing

For non-critically ill hospitalized patients with type 2 diabetes: 1

• Use a total daily insulin dose between 0.3 and 0.5 units/kg 1
• Divide with half allocated to basal insulin (given 1-2 times daily) and half to rapid-acting insulin before meals 1
• Critical pitfall: Never use sliding scale insulin alone in hospitalized patients with established diabetes—it leads to poor glycemic control 1

Transitioning from IV to Subcutaneous Insulin

When moving stable ICU patients to subcutaneous insulin: 1

• Calculate TDD as the total amount of IV insulin infused over the previous 12 hours, multiplied by 2 1
• Example: If patient received average of 1.5 units/hour, estimated daily dose = 36 units/24 hours 1
• Give half as basal insulin and divide the other half among three meals as rapid-acting insulin 1

Enteral/Parenteral Nutrition

For patients receiving tube feedings who require insulin: 1

• Calculate 1 unit of insulin for every 10-15 grams of carbohydrate in the formula 1
• For continuous feeds: use NPH insulin every 8-12 hours or regular insulin every 6 hours 1
• For bolus feeds: give regular or rapid-acting insulin before each feeding 1
• Critical safety point: Patients with type 1 diabetes must continue basal insulin even if feedings are discontinued; start 10% dextrose infusion immediately if nutrition is interrupted 1

Glucocorticoid-Induced Hyperglycemia

For patients on daily prednisone or prednisolone: 1

• Expect hyperglycemia pattern with normal/mild fasting levels, increasing afternoon hyperglycemia, and evening peaks 1
• Consider dosing NPH insulin in the morning for steroid-induced hyperglycemia 1

Advanced Calculations for Insulin Pumps

Carbohydrate-to-Insulin Ratio

The carbohydrate ratio has diurnal variation: 3

• At breakfast: CIR = 300/TDD 3
• At lunch and supper: CIR = 400/TDD 3
• This accounts for increased insulin resistance in the morning hours 3

Correction Factor

• Glucose correction factor = 1960/TDD 4
• This formula helps determine how much one unit of insulin will lower blood glucose 4

Basal Rate for Pumps

• Basal units/day = TDD × 0.48 (approximately 48% of TDD, not the traditional 50%) 4
• This reflects actual clinical practice patterns in patients with optimal glucose control 4

Key Safety Considerations

Monitor for these common causes of hypoglycemia: 1

• Sudden reduction in corticosteroid dose
• Reduced oral intake or emesis
• Inappropriate timing of short/rapid-acting insulin relative to meals
• Reduced IV dextrose infusion rate
• Unexpected interruption of enteral/parenteral feedings
• Delayed or missed blood glucose checks

Important caveat: 84% of patients who experience severe hypoglycemia (<40 mg/dL) had a preceding episode of any hypoglycemia (<70 mg/dL) during the same admission, yet 75% did not have their basal insulin dose adjusted 1

When to consider insulin as first-line therapy: 1

• Symptoms of hyperglycemia are present
• A1C >10% (>86 mmol/mol) or blood glucose ≥300 mg/dL (≥16.7 mmol/L)
• Type 1 diabetes is a diagnostic possibility