When is insulin indicated in type 2 diabetes mellitus (T2DM)?

Indications for Insulin Therapy in Type 2 Diabetes Mellitus

Insulin therapy should be initiated in patients with type 2 diabetes who are not achieving glycemic goals with lifestyle intervention and oral hypoglycemic agents within 3 months of recognition of treatment failure, or immediately in patients with severe hyperglycemia (HbA1c >10% or blood glucose ≥300 mg/dL) with symptoms. 1

Primary Indications for Insulin Therapy

1. Failure of Oral Medications

   • When HbA1c targets are not achieved after 3 months of optimized oral medication therapy 1
   • Ideally initiated within 3 months of recognizing failure of lifestyle and oral medication combinations 1

2. Severe Hyperglycemia at Diagnosis or During Treatment

   • HbA1c >9.0% or FPG ≥11.1 mmol/L (≥200 mg/dL) with symptomatic hyperglycemia 1
   • HbA1c >10% (>86 mmol/mol) or blood glucose ≥300 mg/dL (≥16.7 mmol/L) 1
   • Evidence of ongoing catabolism (unexpected weight loss) 1

3. Specific Clinical Scenarios

   • Acute illness or surgery requiring tight glucose control 2
   • Pregnancy 2
   • Contraindications to oral hypoglycemic agents 1
   • Need for flexible therapy 2

Insulin Initiation Approaches

For Patients Failing Oral Medications

1. Basal Insulin

   • Starting dose: 0.1-0.2 units/kg/day or 10 units once daily 3
   • Usually intermediate-acting human insulin or long-acting insulin analogs 1
   • Continue metformin when starting insulin to reduce weight gain, lower insulin dose requirements, and reduce hypoglycemia risk 2

2. Premixed Insulin

   • Alternative to basal insulin
   • 1-3 times daily dosing 1
   • Particularly useful when both fasting and postprandial glucose are elevated

For Severe Hyperglycemia

1. Short-term Intensive Insulin Therapy
   • 2 weeks to 3 months duration for newly diagnosed patients with HbA1c >9.0% 1
   • Options include:
     • Multiple daily injections (basal + prandial)
     • Premixed insulin 2-3 times daily
     • Continuous subcutaneous insulin infusion (CSII) 1

Insulin Intensification

When basal insulin alone is insufficient to achieve glycemic targets:

1. Add Prandial (Bolus) Insulin

   • Start with one injection at the largest meal 4
   • Consider when basal insulin dose exceeds or approaches 0.5 units/kg/day 1, 4
   • Gradually add additional mealtime injections if needed

2. Switch to Multiple Daily Injections

   • Basal + prandial insulin (2-4 injections per day) 1
   • Mimics physiologic insulin secretion pattern

3. Consider GLP-1 RA with Insulin

   • Combination provides greater glycemic effectiveness with beneficial effects on weight and hypoglycemia risk 1
   • May allow for reduction in insulin requirements 4

Important Considerations

• Monitor for Overbasalization: Signs include basal dose >0.5 units/kg/day, significant glucose differentials between bedtime and morning, hypoglycemia, or high glycemic variability 1

• Avoid Abrupt Discontinuation: Oral medications should not be abruptly discontinued when starting insulin due to risk of rebound hyperglycemia 2

• Minimize Adverse Effects:

  • Hypoglycemia risk can be reduced by using long-acting insulin analogs instead of NPH 5
  • Weight gain can be minimized by combining insulin with metformin, GLP-1 RAs, or SGLT2 inhibitors 5

• Insulin Preference in Special Situations:

  • For patients with severe insulin resistance, U-500 may be more effective than U-100 insulin 5
  • Insulin detemir may offer weight advantages over glargine or NPH 5

Monitoring and Titration

• Use fasting plasma glucose values to titrate basal insulin 2
• Use both fasting and postprandial glucose values to titrate mealtime insulin 2
• Increase frequency of blood glucose monitoring during insulin initiation and dose adjustments 3

Common Pitfalls to Avoid

1. Delayed Insulin Initiation: Delaying insulin therapy when indicated can lead to prolonged hyperglycemia and increased risk of complications 4

2. Inadequate Dose Titration: Timely dose adjustments are essential for achieving glycemic targets 1

3. Ignoring Patient Education: Proper training on injection technique, site rotation, and hypoglycemia management is crucial 2

4. Neglecting Weight Management: Continue weight management efforts even after insulin initiation 1

5. Overlooking Combination Therapy: Using insulin with appropriate oral agents can improve outcomes and reduce insulin requirements 2

By following these guidelines, clinicians can effectively initiate and manage insulin therapy in patients with type 2 diabetes to improve glycemic control and reduce the risk of diabetes-related complications.