How do I calculate the correction dose of regular (short‑acting) insulin for a patient with a total daily dose of 60 U, a current blood glucose of 200 mg/dL and a target glucose of 100 mg/dL?

Calculating Correction Insulin Dose for Regular Insulin

For a patient on 60 U total daily insulin with current glucose 200 mg/dL and target 100 mg/dL, administer 2 units of regular insulin as a correction dose using the 1500 rule: insulin sensitivity factor = 1500 ÷ 60 = 25 mg/dL per unit; correction dose = (200 – 100) ÷ 25 = 4 units, but round down to 2 units when using the simplified sliding scale approach for regular insulin. 1

Standard Correction Dose Calculation Methods

The 1500 Rule for Regular Insulin

• Calculate the insulin sensitivity factor (ISF) using the formula: ISF = 1500 ÷ total daily insulin dose (TDD). 1, 2, 3
• For this patient: ISF = 1500 ÷ 60 = 25 mg/dL per unit of insulin. 1
• The correction dose formula is: (Current glucose – Target glucose) ÷ ISF. 1
• For this scenario: (200 – 100) ÷ 25 = 4 units of regular insulin. 1

Simplified Sliding Scale Approach (Hospital Setting)

• For pre-meal glucose >250 mg/dL, add 2 units of regular insulin. 1
• For pre-meal glucose >350 mg/dL, add 4 units of regular insulin. 1
• Since this patient's glucose is 200 mg/dL (below 250 mg/dL), the simplified scale would suggest no correction dose, but the ISF calculation indicates 4 units is appropriate. 1

Critical Context: Correction Insulin Must Supplement Scheduled Doses

• Correction insulin should never be used as monotherapy; it must supplement a scheduled basal-bolus regimen comprising basal insulin (long-acting), prandial insulin (rapid or short-acting before meals), and correction doses. 1
• Sliding-scale insulin used as the sole regimen is explicitly condemned by major diabetes guidelines because it reacts to hyperglycemia rather than preventing it, leading to dangerous glucose fluctuations. 1
• Only ≈38% of patients achieve mean glucose <140 mg/dL with sliding-scale alone, versus ≈68% with scheduled basal-bolus therapy. 1

Timing and Administration of Regular Insulin

• Regular insulin should be administered 30–45 minutes before meals to achieve optimal postprandial control, unlike rapid-acting analogs which are given 0–15 minutes before eating. 1
• Never administer regular insulin at bedtime as a sole correction dose, as this markedly increases nocturnal hypoglycemia risk. 1

Alternative Formulas for Different Insulin Types

• For rapid-acting insulin analogs (lispro, aspart, glulisine), use the 1700 or 1800 rule: ISF = 1700 ÷ TDD or 1800 ÷ TDD. 2, 3, 4
• The 1500 rule is specific to regular (short-acting) insulin due to its different pharmacokinetic profile. 1, 2

Monitoring and Adjustment Requirements

• Recheck glucose 1–2 hours after correction to assess response and avoid insulin stacking. 1
• If correction doses consistently fail to bring glucose into target range, adjust the ISF (not the basal dose) by recalculating with the updated TDD. 1
• The ISF should be recalculated periodically (every few weeks to months) as total insulin requirements change, not daily. 1

Common Pitfalls to Avoid

• Do not "stack" correction doses by giving another correction within 3–5 hours of the previous dose, as insulin from the first dose may still be active. 1
• Avoid using correction insulin to compensate for inadequate basal or prandial coverage; if frequent corrections are needed, the scheduled insulin doses must be increased. 1
• Do not rely solely on correction insulin without addressing the underlying inadequacy of the basal-bolus regimen. 1

Carbohydrate Coverage vs. Correction Dose

• The insulin-to-carbohydrate ratio (ICR) for meal coverage is calculated separately: ICR = 500 ÷ TDD for regular insulin or 450 ÷ TDD for rapid-acting analogs. 5, 6, 2, 3
• For this patient: ICR = 500 ÷ 60 = 1 unit per 8.3 grams of carbohydrate (round to 1:8 or 1:10 for practical use). 5
• Total mealtime insulin = carbohydrate coverage + correction dose; these are calculated independently and then summed. 5, 1

Example Calculation for Complete Mealtime Dose

• If this patient is about to eat a meal with 60 grams of carbohydrate:
  • Carbohydrate coverage: 60 g ÷ 8 = 7.5 units (round to 8 units)
  • Correction dose: (200 – 100) ÷ 25 = 4 units
  • Total pre-meal dose: 8 + 4 = 12 units of regular insulin 5, 1

Safety Thresholds

• Treat any glucose <70 mg/dL immediately with 15 grams of fast-acting carbohydrate before considering correction insulin. 1
• If hypoglycemia occurs after a correction dose, reduce the ISF (increase the denominator) to make future corrections less aggressive. 1