The 1800 Rule & 1500 Rule for Correction Dosing
The Insulin Sensitivity Factor (ISF), also called the correction factor, represents how many points (in mg/dL or mmol/L) one unit of rapid-acting or short-acting insulin will lower blood glucose over its active duration.
Example: If TDD is 45 units → ISF = 1800 ÷ 45 = 40 mg/dL per unit (or 2.2 mmol/L per unit).
Example: If TDD is 50 units → ISF = 1500 ÷ 50 = 30 mg/dL per unit (or 1.7 mmol/L per unit).
The 500 Rule & 450 Rule for Meal Boluses
The Insulin-to-Carbohydrate Ratio (ICR) indicates how many grams of carbohydrate are metabolized or covered by one unit of mealtime rapid or regular insulin.
Example: If TDD is 50 units → ICR = 500 ÷ 50 = 10g carbs per 1 unit of insulin (1:10 ratio).
Example: If TDD is 45 units → ICR = 450 ÷ 45 = 10g carbs per 1 unit of insulin.
Insulin On Board (IOB) Decay Models
Administering a correction dose while a prior bolus is still metabolizing causes insulin stacking, the leading cause of postprandial hypoglycemia. Insulin Point models physiological clearance to calculate remaining active units.
Subcutaneous dissociation from hexamers into active monomers.
Maximum glucose disposal rate (GDR) and receptor occupancy.
Terminal hepatic and renal degradation tail.
Total Net Bolus Calculation Formula
Notice that active IOB is subtracted exclusively from the correction bolus, ensuring you do not under-dose the meal carbohydrates. In Insulin Point's calculator, you can toggle Stacking Protection on or off depending on whether you have taken an insulin dose recently.
When glucose is below target, most pump bolus calculators apply a reverse correction: the amount of insulin that would lower you from target to your current level is taken off the meal dose. Example: 85 mg/dL with a 100 mg/dL target and ISF 40 gives (100 − 85) ÷ 40 = 0.38 units less. Insulin Point applies this automatically and never lets the total go below zero. Below 70 mg/dL (3.9 mmol/L), treat the low first and recheck before taking any meal insulin.
Weight-Based Starting Dosing & Basal-Bolus Splits
When initiating intensive insulin therapy, initial Total Daily Dose (TDD) is calculated from patient weight and clinical status, typically split 50% basal (background) and 50% prandial (bolus divided across 3 meals).
| Clinical Scenario | Starting Dose (units/kg/day) | Basal / Bolus Split | Key Clinical Considerations |
|---|---|---|---|
| Type 1 Honeymoon / Sensitive | 0.2 – 0.4 u/kg | 50% / 50% | Residual endogenous beta-cell production; high hypoglycemia risk. |
| Standard Adult Type 1 / Typical | 0.4 – 0.6 u/kg | 50% / 50% | Standard ADA starting benchmark for established intensive therapy. |
| Type 2 Insulin-Resistant / Obese | 0.6 – 1.0+ u/kg | 40% / 60% or 50% / 50% | Marked peripheral insulin resistance; often requires concentrated U-200/U-500. |
| Adolescent Growth Spurt / Pregnancy | 1.0 – 1.5 u/kg | 45% / 55% | Elevated growth hormone or placental hormones inducing acute resistance. |
Official Manufacturer Beyond-Use-Dating (Room Temperature / In-Use Limits)
Once an insulin vial, pen, or cartridge is unsealed or removed from refrigerated storage (36°F–46°F / 2°C–8°C), molecular peptide degradation accelerates. Room temperature limits strictly cap the clinical days supply.
| Insulin Product | Class & Concentration | Package Configuration | Room Temp Limit (BUD) | Refrigerated Shelf Life |
|---|---|---|---|---|
| Humalog (insulin lispro) | Rapid Analog (U-100, U-200) | 10 mL vial / 5x3 mL KwikPen | 28 Days | Until Expiration Date |
| Novolog / Fiasp (insulin aspart) | Rapid / Ultra-Rapid (U-100) | 10 mL vial / 5x3 mL FlexPen | 28 Days | Until Expiration Date |
| Apidra (insulin glulisine) | Rapid Analog (U-100) | 10 mL vial / 5x3 mL SoloStar | 28 Days | Until Expiration Date |
| Lantus / Basaglar / Semglee | Long-Acting Glargine (U-100) | 10 mL vial / 5x3 mL pens | 28 Days | Until Expiration Date |
| Toujeo (glargine U-300) | Concentrated Basal (U-300) | 3x1.5 mL SoloStar / 2x3 mL Max | 56 Days (8 Weeks) | Until Expiration Date |
| Levemir (insulin detemir) | Long-Acting Basal (U-100) | 5x3 mL FlexTouch | 42 Days (6 Weeks) | Until Expiration Date |
| Tresiba (insulin degludec) | Ultra-Long Basal (U-100, U-200) | 5x3 mL or 3x3 mL FlexTouch | 56 Days (8 Weeks) | Until Expiration Date |
| Humulin R U-500 | Concentrated Regular (U-500) | 20 mL vial / 2x3 mL KwikPen | 40 Days (Vial) / 28 Days (Pen) | Until Expiration Date |
Clinical Citations & Practice Standards
- American Diabetes Association (ADA). Standards of Care in Diabetes — Pharmacologic Approaches to Glycemic Treatment. Diabetes Care.
- Walsh J, Roberts R. Pumping Insulin: Everything You Need for Success with an Insulin Pump. San Diego: Torrey Pines Press.
- Scheiner G. Think Like a Pancreas: A Practical Guide to Managing Diabetes with Insulin. Da Capo Lifelong Books.
- United States Pharmacopeial Convention (USP). General Chapter <797> Pharmaceutical Compounding — Sterile Preparations and Beyond-Use Dating (BUD) in Ambulatory Care.
- Endocrine Society. Clinical Practice Guideline: Management of Hyperglycemia in Hospitalized Patients in Non-Critical Care Settings.
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