Insulin Dosing

1. Components of an Insulin Regimen

Insulin regimens mimic (or fail to mimic) the way a healthy pancreas delivers insulin. A pancreas provides:

  • Basal insulin - continuous, low-level insulin secretion (day and night to control hepatic glucose release, especially overnight).

    • Goal: smooth background effect, ideally no peaks.

    • Examples: glargine (Lantus, Toujeo, Semglee, Basaglar), detemir (Levemir), degludec (Tresiba).

    • Dosed once daily (some, such as Levemir, may require BID).

  • Bolus insulin - surges of insulin around meals or in response to glucose spikes.

    • Goal: cover meals and correct hyperglycemia in real time.

    • Examples: lispro (Humalog, Admelog, Lyumjev), aspart (Novolog, Fiasp), glulisine (Apidra), regular insulin (Humulin R — slower, less commonly used).

  • Practical Considerations

    • 50/50 rule: As a starting point, total daily insulin is roughly split into 40-50% basal and 50-60% bolus.

    • Real life variation: Many patients creep into “overbasalization” (≥70% basal insulin, <30% bolus) if afraid of hypoglycemia or avoiding carb counting.

    • Rounding & devices: Syringe (nearest 0.5–1 unit), pens (nearest 1 unit), pumps (decimal dosing possible).

2. Determining an Appropriate Insulin Regimen

  1. Basal only

    • Once daily long-acting insulin.

    • Usually for early type 2 diabetes, as patients still make some endogenous insulin.

    • Pros: simple, only 1 injection/day.

    • Cons: does not cover food or prevent post-meal hyperglycemia in type 1.

    • Not sufficient for type 1 diabetes (unless honeymoon period or terminal care).

  2. Two-injection regimen (premix insulin or split mixed)

    • Mix of intermediate/rapid (e.g., NPH + Regular or NPH + Rapid) at breakfast and dinner.

    • Covers basal + meals together, but inflexible: patient has to eat consistently timed meals in consistent amounts.

    • Best for: patients with structured schedules, limited resources, who cannot carb count.

    • Less common in modern type 1 management.

  3. Basal-bolus regimen (modern standard of care for type 1)

    • Long-acting once daily for basal needs.

    • Rapid insulin before each meal, guided by carb ratio and ISF.

    • Flexible, physiologic, allows adjusting doses depending on carbs/activity.

  4. Fixed dose regimen

    • Provider prescribes set insulin doses with each meal (e.g., 5 units breakfast, 10 units lunch, 8 units dinner).

    • No flexibility: patient must eat to match insulin rather than insulin matching food.

    • Historically common, but less optimal for active patients.

  5. Sliding scale

    • Reactive: bolus insulin only given based on glucose level (e.g., “Give 4 units if glucose is 200-250”).

    • Lacks proactive carb coverage, often leads to highs and lows.

    • ❌ Outdated if used alone, but can be used in hospital or layered on top of basal-bolus for corrections.

3. Calculations

  • Total Daily Dose (TDD) = - 0.5 × body weight (kg) = TDD 50% → Basal, 50% → Bolus

  • Carb Ratio (ICR) = Rule of 500 (rapid insulin).

    • amount of bolus insulin to dispose 4-30 g of carb based on insulin sensitivity

    • lower ratio means more insulin needed to cover type 1 diabetes

    • 500 ÷ TDD = grams of carb covered by 1 unit.

    • Rounding - Whole numbers unless <5, Decimal end round in direction of easier numbers

  • Insulin Sensitivity Factor (ISF) = Rule of 1800 (rapid insulin).

    • estimated point drop in mg/dL of BG for every correction taken in type 1 diabetes

    • 1800 ÷ TDD = glucose drop per 1 unit insulin.

    • typically goal is somewhere between 100-120 mg/dL for us 120

    • Rounding

      • should end in a 0 or 5 if not round in direction of easier math