How do I calculate the insulin dose for a 70‑kg adult with type 1 diabetes?

Calculating Insulin Dose for a 70‑kg Adult with Type 1 Diabetes

For a metabolically stable 70‑kg adult with type 1 diabetes, start with a total daily dose (TDD) of 0.5 units/kg/day (35 units), allocating 40–50% (14–18 units) as once‑daily basal insulin and 50–60% (17–21 units) as rapid‑acting prandial insulin divided across three meals (≈6–7 units per meal). 1

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Step 1: Calculate Total Daily Insulin Requirement

• Standard starting dose: 0.5 units/kg/day for metabolically stable type 1 diabetes patients 1
• For a 70‑kg adult: 0.5 × 70 = 35 units/day total 1
• Acceptable range: 0.4–1.0 units/kg/day (28–70 units) depending on clinical context 1

Special Situations Requiring Dose Adjustment

• Honeymoon phase or residual beta‑cell function: 0.2–0.6 units/kg/day (14–42 units) 1
• Puberty or acute illness: May approach 1.0–1.5 units/kg/day (70–105 units) due to hormonal insulin resistance 1, 2
• Immediately post‑ketoacidosis: Higher weight‑based dosing required 1

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Step 2: Divide Between Basal and Prandial Insulin

Basal Insulin (Long‑Acting)

• Allocation: 40–50% of TDD 1
• For 35 units TDD: 14–18 units once daily 1
• Timing: Typically given at bedtime or same time each day 3
• Options: Insulin glargine (Lantus), detemir (Levemir), or degludec (Tresiba) 4, 3

Prandial Insulin (Rapid‑Acting)

• Allocation: 50–60% of TDD 1
• For 35 units TDD: 17–21 units total, divided among three meals 1
• Per‑meal dose: ≈6–7 units before breakfast, lunch, and dinner 1
• Timing: Administer 0–15 minutes before meals 5, 4
• Options: Lispro (Humalog), aspart (NovoLog), or glulisine (Apidra) 4

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Step 3: Titration Protocols

Basal Insulin Titration

• Target fasting glucose: 80–130 mg/dL 4, 1
• If fasting glucose 140–179 mg/dL: Increase basal by 2 units every 3 days 4, 1
• If fasting glucose ≥180 mg/dL: Increase basal by 4 units every 3 days 4, 1
• If hypoglycemia (<70 mg/dL) occurs: Reduce dose by 10–20% immediately 4, 1

Prandial Insulin Titration

• Target postprandial glucose: <180 mg/dL at 2 hours after meals 4, 1
• Adjustment: Increase each meal dose by 1–2 units every 3 days based on 2‑hour postprandial readings 4, 1, 2
• If hypoglycemia occurs: Reduce the implicated meal dose by 10–20% 4, 1

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Step 4: Advanced Dosing—Carbohydrate Counting

Insulin‑to‑Carbohydrate Ratio (ICR)

• Formula for rapid‑acting analogs: ICR = 450 ÷ TDD 4, 2
• For 35 units TDD: 450 ÷ 35 = ≈13 g carbohydrate per 1 unit insulin 6
• Breakfast typically requires more insulin: Use 300 ÷ TDD (≈9 g/unit) due to dawn phenomenon 6
• Lunch and dinner: Use 400 ÷ TDD (≈11 g/unit) 6

Correction Factor (Insulin Sensitivity Factor)

• Formula: CF = 1500 ÷ TDD 4, 2, 7
• For 35 units TDD: 1500 ÷ 35 = ≈43 mg/dL drop per 1 unit insulin 7
• Use for correction doses: (Current glucose – Target glucose) ÷ CF 4

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Step 5: Monitoring Requirements

• Daily fasting glucose during titration to guide basal adjustments 4, 1
• Pre‑meal glucose before each meal to calculate correction doses 4
• 2‑hour postprandial glucose after each meal to assess prandial adequacy 4, 1
• HbA1c every 3 months during intensive titration 4, 2

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Critical Pitfalls to Avoid

• Never use sliding‑scale insulin as monotherapy in type 1 diabetes—it can precipitate diabetic ketoacidosis 4, 1
• Never give rapid‑acting insulin at bedtime as a sole correction dose—markedly raises nocturnal hypoglycemia risk 4, 1
• Never delay insulin initiation or prescribe inadequate doses in type 1 diabetes—immediate basal‑bolus therapy is required 4
• Do not mix or dilute insulin detemir with any other insulin or solution 3

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Practical Example for 70‑kg Adult

Component	Calculation	Dose
Total Daily Dose	0.5 × 70 kg	35 units
Basal Insulin	45% of 35 units	16 units once daily
Prandial Insulin	55% of 35 units	19 units total
• Breakfast	≈33% of prandial	6 units
• Lunch	≈33% of prandial	6 units
• Dinner	≈33% of prandial	7 units

1

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Alternative Calculation Methods

Weight‑Based Basal Dosing (Insulin Detemir)

• Type 1 diabetes starting dose: Approximately one‑third to one‑half of TDD as basal insulin 3
• Initial TDD calculation: 0.2–0.4 units/kg (14–28 units for 70 kg) 3
• Basal portion: 5–14 units once or twice daily 3

Pump Therapy Calculations

• Basal insulin: Approximately 30–50% of TDD delivered as continuous infusion 6, 7
• For 35 units TDD: 11–18 units as basal rate (≈0.5–0.75 units/hour) 6
• ICR for pump: 300 ÷ TDD at breakfast, 400 ÷ TDD at lunch/dinner 6
• CF for pump: 1500 ÷ TDD 7

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When to Adjust the Standard Formula

• Higher doses needed: Puberty, pregnancy, acute illness, steroid therapy (40–60% increase) 1, 2
• Lower doses needed: Honeymoon phase, young children, elderly, renal impairment 1
• Twice‑daily basal dosing: May be required if once‑daily glargine or detemir does not provide 24‑hour coverage 4, 3