How should insulin be prescribed for adult patients with type 2 diabetes mellitus?

How to Prescribe Insulin in Type 2 Diabetes

GLP-1 receptor agonists (including dual GIP/GLP-1 agonists) are now preferred over insulin for most patients with type 2 diabetes who need injectable therapy, unless there is evidence of insulin deficiency, severe hyperglycemia (A1C >10% or glucose ≥300 mg/dL), or symptomatic hyperglycemia. 1

When to Initiate Insulin

Immediate Insulin Indications

Insulin should be started immediately when: 1

• A1C >10% (>86 mmol/mol) or blood glucose ≥300 mg/dL (≥16.7 mmol/L)
• Symptomatic hyperglycemia present (polyuria, polydipsia, weight loss)
• Evidence of ongoing catabolism (unexpected weight loss, ketosis)

Insulin as Add-On Therapy

Consider insulin when: 1

• A1C remains above target after 3-6 months of optimized oral agents
• A1C ≥8.5% makes it unlikely other agents will provide sufficient benefit 1
• Progressive beta-cell failure despite combination therapy

How to Start Insulin

Initial Dosing Strategy

Begin with basal insulin at 0.1-0.2 units/kg/day (typically 10 units for most patients), or 0.3-0.4 units/kg/day if severely hyperglycemic (glucose >300 mg/dL). 1

Basal Insulin Options

• Long-acting analogues (glargine, detemir, degludec): Associated with less nocturnal hypoglycemia than NPH 1
• NPH insulin: More affordable alternative, though with higher hypoglycemia risk 1
• Administer at bedtime or timing based on patient's glucose profile 1

Titration Protocol

Increase basal insulin by 2-4 units (or 10-15% of current dose) once or twice weekly until fasting glucose reaches target (typically 80-130 mg/dL). 1 Patients can self-titrate using algorithms like:

• Fasting glucose <4.4 mmol/L (80 mg/dL): decrease 2 units
• 4.4-7.0 mmol/L (80-126 mg/dL): no change
• 7.1-10.0 mmol/L (127-180 mg/dL): increase 2 units

• 10.0 mmol/L (>180 mg/dL): increase 4 units 2

Combination Therapy Considerations

Continue Metformin

Metformin should be continued when starting insulin as it reduces weight gain, lowers insulin requirements, and decreases hypoglycemia risk compared to insulin alone. 1, 3

Adjust High-Risk Medications

Reduce or discontinue sulfonylureas and meglitinides when starting insulin to minimize hypoglycemia risk. 1

Preferred Combination: Insulin + GLP-1 RA

If insulin is used, adding a GLP-1 RA (or dual GIP/GLP-1 RA) is recommended for superior glycemic control, weight benefits, and reduced hypoglycemia. Insulin doses should be reassessed and often reduced when adding GLP-1 RA. 1

Intensifying Insulin Therapy

When to Add Prandial Insulin

Consider adding mealtime insulin when: 1

• Fasting glucose at target but A1C remains elevated after 3-6 months of basal insulin
• Basal insulin dose exceeds 0.5 units/kg/day (sign of overbasalization) 1
• Significant postprandial glucose excursions (>180 mg/dL)

Prandial Insulin Options

Start with 4 units or 10% of basal dose before the largest meal, using rapid-acting analogues (lispro, aspart, glulisine). 1 Alternatively, switch to twice-daily premixed insulin (70/30 NPH/regular or analogue mixes). 1

Monitoring for Overbasalization

Watch for these warning signs: 1

• Basal dose >0.5 units/kg/day
• Large bedtime-to-morning glucose differential
• Hypoglycemia episodes (aware or unaware)
• High glycemic variability

Special Populations and Considerations

Cardiovascular and Renal Disease

• Heart failure patients: Prioritize SGLT2 inhibitors over insulin 1
• CKD (eGFR 20-60): Use SGLT2 inhibitors first 1
• Advanced CKD (eGFR <30): GLP-1 RA preferred over insulin 1

Cost Considerations

For patients with financial barriers, human insulin (NPH and regular) remains an acceptable lower-cost option, though with higher hypoglycemia risk and less flexible dosing. 1

Critical Pitfalls to Avoid

• Do not delay insulin intensification: Months of uncontrolled hyperglycemia should be specifically avoided 1
• Do not use insulin as a threat: Frame it as expected disease progression, not punishment 1
• Do not abruptly stop oral agents: Risk of rebound hyperglycemia 3
• Do not combine DPP-4 inhibitors with GLP-1 RA: No additional benefit 1
• Avoid saxagliptin and alogliptin in heart failure: FDA warning for increased heart failure risk 1

Patient Education Requirements

Essential education includes: 1

• Self-monitoring of blood glucose technique
• Insulin injection technique and storage
• Hypoglycemia recognition and treatment
• Sick day management
• Self-titration algorithms