When and how should insulin be initiated in patients with type 2 diabetes mellitus (T2DM)?

Initiating Insulin in Type 2 Diabetes Mellitus

Insulin therapy should be initiated in patients with T2DM who are not achieving glycemic goals with lifestyle intervention and oral hypoglycemic agents, ideally within 3 months of recognition of treatment failure. 1

When to Initiate Insulin

Immediate Insulin Initiation Required:

• Newly diagnosed T2DM with:
  • HbA1c > 9.0% or FPG ≥ 11.1 mmol/L with symptomatic hyperglycemia 1
  • Blood glucose ≥250 mg/dL 1
  • Presence of ketosis or diabetic ketoacidosis
  • Acute illness or surgery
  • Pregnancy
  • Glucose toxicity

Delayed Insulin Initiation (After Oral Agents):

• Failure to achieve target HbA1c < 7.0% after 3 months of optimized oral hypoglycemic therapy 1
• Contraindications to oral antidiabetic medications
• Need for flexible therapy

How to Initiate Insulin

Initial Insulin Regimen Options:

1. Basal Insulin Approach (Preferred first-line insulin strategy):

   • Start with intermediate-acting human insulin (NPH) or long-acting insulin analogs (glargine, detemir, degludec)
   • Starting dose: 10 units or 0.1-0.2 units/kg once daily 1
   • Administer at bedtime or any consistent time of day 2
   • Continue metformin and consider discontinuing insulin secretagogues 1
   • Titrate dose by 2-4 units every 3-7 days until target fasting glucose is reached

2. Premixed Insulin Approach:

   • Premixed human insulin or premixed insulin analogs
   • Typically administered 1-3 times daily 1
   • Consider in patients with regular meal patterns or those who need simplified regimens

3. Short-term Intensive Insulin Therapy:

   • For newly diagnosed patients with HbA1c > 9.0% or FPG ≥ 11.1 mmol/L 1
   • Duration: 2 weeks to 3 months
   • May help reverse glucose toxicity

Insulin Intensification When Needed:

If basal insulin alone doesn't achieve glycemic targets:

1. Add mealtime (bolus) insulin:

   • Start with one injection of rapid-acting insulin with largest meal
   • Progress to multiple daily injections as needed (basal-bolus regimen)
   • Typically 40-50% of total daily insulin as bolus insulin 3

2. Switch to premixed insulin 2-3 times daily 1

3. Consider continuous subcutaneous insulin infusion (CSII) for selected patients 1

Monitoring and Titration

• Monitor HbA1c every 3 months 1
• Self-monitoring of blood glucose:
  • Fasting glucose to titrate basal insulin
  • Pre- and post-prandial glucose to titrate mealtime insulin
• Equip patients with an algorithm for self-titration of insulin doses 1
• Intensify treatment if glycemic targets are not met

Special Considerations

• Hypoglycemia risk: Long-acting insulin analogs (particularly degludec) have lower risk of hypoglycemia compared to NPH insulin 4
• Weight gain: Combining insulin with metformin may result in less weight gain 5
• Injection technique: Use shortest available needles (4-6mm) and rotate injection sites to prevent lipohypertrophy 5
• Barriers to initiation: Address fear of hypoglycemia, injection anxiety, and perceived treatment failure 6

Common Pitfalls to Avoid

1. Delayed insulin initiation: Don't wait too long to start insulin when oral agents fail
2. Abrupt discontinuation of oral medications: Continue metformin when starting insulin 5
3. Inadequate dose titration: Failure to adjust insulin doses frequently enough
4. Ignoring patient education: Patients need thorough education on injection technique, glucose monitoring, and hypoglycemia management
5. Overlooking lifestyle modifications: Continue to emphasize diet and exercise alongside insulin therapy

By following this structured approach to insulin initiation in T2DM, clinicians can effectively improve glycemic control and reduce the risk of diabetes-related complications while minimizing adverse effects such as hypoglycemia.