What is the recommended initial insulin regimen for managing type 1 diabetes mellitus?

Treatment for Type 1 Diabetes Mellitus

Most people with type 1 diabetes should be treated with multiple-dose insulin (MDI) injections—three to four injections per day of basal and prandial insulin—or continuous subcutaneous insulin infusion (CSII), using insulin analogs to reduce hypoglycemia risk. 1

Initial Insulin Regimen

Starting Dose Calculation

• Begin with 0.5 units/kg/day as the total daily insulin dose (TDD) for metabolically stable patients 2
• The acceptable range is 0.4–1.0 units/kg/day 1, 2
• For patients presenting with diabetic ketoacidosis, use higher weight-based dosing than the standard 0.5 units/kg/day 2
• Young children and those in the "honeymoon period" with residual beta-cell function may require lower doses of 0.2–0.6 units/kg/day 2

Distribution Between Basal and Prandial Insulin

• Divide the TDD as approximately 50% basal insulin and 50% prandial insulin 1, 2
• The basal component provides continuous background insulin coverage throughout the 24-hour day 1
• The prandial component is divided among three meals to control postprandial glucose excursions 1, 2

Insulin Types and Administration

Basal Insulin Options

• Use long-acting insulin analogs (glargine, detemir, or degludec) rather than NPH insulin 1
• These analogs have longer duration of action with flatter, more constant plasma concentrations and reduced hypoglycemia risk compared to NPH 1
• Administer basal insulin once daily at the same time each day 1, 3
• Insulin degludec requires only once-daily dosing with a terminal half-life of approximately 25 hours 4

Prandial Insulin Options

• Use rapid-acting insulin analogs (aspart, lispro, or glulisine) rather than regular human insulin 1, 5
• Administer 0–15 minutes before meals for optimal postprandial glucose control 1, 5
• Rapid-acting analogs have quicker onset and peak with shorter duration of action than regular human insulin 1
• Faster-acting insulin aspart offers better postprandial glucose coverage 1

Patient Education Requirements

Carbohydrate Counting and Dose Adjustment

• Educate patients on how to match prandial insulin dose to carbohydrate intake, premeal blood glucose, and anticipated activity 1
• Use the insulin-to-carbohydrate ratio (ICR) to determine mealtime doses 6
• Calculate ICR using the formula: 450 ÷ TDD for rapid-acting analogs 6
• Use the insulin sensitivity factor (ISF) for correction doses, calculated as 1500 ÷ TDD 6

Self-Monitoring Requirements

• Perform self-monitoring of blood glucose at least four times per day (before each meal and at bedtime) 7
• More frequent monitoring may be needed during illness, exercise, or when adjusting doses 1
• Consider continuous glucose monitoring to improve glycemic control and reduce hypoglycemia 5

Hypoglycemia Recognition and Treatment

• Treat any glucose <70 mg/dL immediately with 15 grams of fast-acting carbohydrate 6
• Recheck glucose in 15 minutes and repeat treatment if needed 6
• Educate patients to always carry a source of fast-acting carbohydrates 6
• Scrupulous avoidance of hypoglycemia for 2–3 weeks can reverse hypoglycemia unawareness 6

Dose Titration and Adjustment

Basal Insulin Titration

• Adjust basal insulin every 3 days based on fasting glucose patterns 1, 6
• Increase by 2 units if fasting glucose is 140–179 mg/dL 6
• Increase by 4 units if fasting glucose is ≥180 mg/dL 6
• Target fasting glucose: 80–130 mg/dL 1, 6
• If hypoglycemia occurs without clear cause, reduce the dose by 10–20% immediately 6

Prandial Insulin Titration

• Adjust prandial insulin every 3 days based on 2-hour postprandial glucose readings 6
• Increase by 1–2 units or 10–15% if postprandial glucose consistently exceeds target 6
• Target postprandial glucose: <180 mg/dL 6

Special Populations Requiring Dose Adjustments

Higher Insulin Requirements

• Puberty: Insulin requirements increase, often approaching 1.0 units/kg/day or more 1, 2
• Pregnancy: Higher doses are required throughout pregnancy 1, 2
• Medical illness: Acute illness, infections, or inflammation increase insulin needs 2
• Glucocorticoid therapy: May require extraordinary amounts of insulin, with increases in both prandial and correctional insulin 6

Lower Insulin Requirements

• Renal impairment (CKD Stage 5): Reduce total daily insulin dose by 35–40% for type 1 diabetes 6
• Elderly patients (>65 years): Use lower starting doses of 0.1–0.25 units/kg/day to prevent hypoglycemia 6

Continuous Subcutaneous Insulin Infusion (CSII)

When to Consider Insulin Pump Therapy

• Patients not meeting individual glycemic targets despite MDI 5
• Those with frequent or severe hypoglycemia 5
• Pronounced dawn phenomenon 5
• Patient preference when reimbursement is available 5

Pump Settings

• Basal rate: Approximately 40–60% of TDD delivered as continuous basal insulin 6
• Bolus doses: Remainder as patient-activated mealtime boluses 8
• Use rapid-acting insulin analogs exclusively in pumps 8

Glycemic Targets

• HbA1c target: <7.5% (<58 mmol/mol) for all children with type 1 diabetes, including preschool children 9
• HbA1c target: <7% (53 mmol/mol) for most nonpregnant adults 5
• Fasting glucose: 80–130 mg/dL 1, 6
• Postprandial glucose: <180 mg/dL 6

Critical Pitfalls to Avoid

• Never use sliding-scale insulin as monotherapy in type 1 diabetes, as it can precipitate diabetic ketoacidosis 6
• Never administer rapid-acting insulin at bedtime as a sole correction dose, as this markedly raises nocturnal hypoglycemia risk 6
• Never dilute or mix insulin degludec with any other insulin or solution 3
• Never transfer insulin from a pen into a syringe for administration 3
• Avoid intramuscular injections, especially with long-acting insulins, as severe hypoglycemia may result 1, 9
• Do not inject into lipohypertrophic areas, as this distorts insulin absorption; practice correct site rotation 9
• Never abruptly discontinue insulin therapy, even during illness with poor oral intake—continue basal insulin and adjust doses appropriately 6

Injection Technique

• Use the shortest needles (4-mm pen and 6-mm syringe needles) as first-line choice in all patients 9
• Recommended injection sites: abdomen, thigh, buttock, and upper arm 1
• Rotate injection sites to prevent lipohypertrophy 1, 9
• Inject into subcutaneous tissue, not intramuscularly 1