How to Start Insulin in Type 2 Diabetes
Begin with basal insulin at 10 units once daily (or 0.1–0.2 units/kg/day) added to metformin, then titrate by 10–15% (approximately 2–4 units) once or twice weekly based on fasting glucose until reaching target of 80–130 mg/dL. 1
When to Initiate Insulin
Immediate insulin initiation is required when:
- HbA1c ≥10% (≥86 mmol/mol) or random glucose ≥300 mg/dL, regardless of symptoms 2, 1
- Marked hyperglycemia with catabolic symptoms (polyuria, polydipsia, weight loss, ketonuria) even at lower HbA1c levels 3, 2, 1
- Ketosis or ketoacidosis is present 1
- Acute illness, surgery, or hospitalization requiring rapid glycemic control 4
Consider insulin when:
- Noninsulin therapy fails to achieve individualized HbA1c targets after 3–6 months 5, 6
- HbA1c ≥7.5% despite optimal oral agents, though newer agents (GLP-1 RAs, SGLT2 inhibitors) should typically be tried first 3, 2
Choosing the Right Basal Insulin
Prefer long-acting basal insulin analogs (glargine U100/U300, degludec U100/U200, or detemir) over NPH insulin because they significantly reduce nocturnal and overall hypoglycemia risk 2, 1, 4. Glargine U300 and degludec demonstrate even less hypoglycemia than glargine U100 or detemir 2.
NPH insulin remains acceptable when cost is prohibitive, though its pharmacodynamic profile is suboptimal 7, 1.
Starting Dose and Titration Protocol
Initial dosing:
- Start at 10 units once daily (or 0.1–0.2 units/kg/day) 1
- Administer at bedtime or any consistent time with newer analogs 3
- Continue metformin and consider maintaining one additional non-insulin agent 1, 4
Titration strategy:
- Increase dose by 10–15% (≈2–4 units) once or twice weekly 1
- Base adjustments on self-monitored fasting blood glucose values 1
- Target fasting plasma glucose of 80–130 mg/dL (4.4–7.2 mmol/L) 1
- Provide patients with a self-titration algorithm at initiation—this significantly improves glycemic control 5, 1
Critical Patient Education Components
Before starting insulin, ensure patients understand:
- Self-monitoring of blood glucose and result interpretation 1, 4
- Hypoglycemia recognition, prevention, and treatment 1, 4
- Injection technique using shortest needles (4-mm pen or 6-mm syringe) to avoid intramuscular injection 4
- Site rotation to prevent lipohypertrophy, which distorts insulin absorption 4
Frame insulin appropriately:
- Explain the progressive nature of type 2 diabetes requiring eventual insulin in most patients 5, 3
- Never describe insulin as punishment or failure—this creates harmful psychological barriers 5, 1
- Emphasize that insulin is a natural treatment progression, not a personal failing 8
Managing Concurrent Medications
Continue metformin when starting insulin—this combination reduces weight gain, lowers insulin requirements, and decreases hypoglycemia compared to insulin alone 4.
Discontinue sulfonylureas once insulin is initiated to avoid compounding hypoglycemia risk 3.
Consider maintaining other agents based on comorbidities:
- SGLT2 inhibitors for heart failure or CKD 6
- GLP-1 receptor agonists for cardiovascular protection or weight management 3, 2
- DPP-4 inhibitors may be continued with basal insulin 7
Avoiding Over-Basalization (Common Pitfall)
Recognize over-basalization early:
- Escalating basal insulin beyond 0.5–1.0 units/kg/day without meaningful fasting glucose improvement indicates over-basalization 1
- This occurs when postprandial hyperglycemia persists despite adequate fasting control
When over-basalization occurs:
- Add prandial insulin (4 units per meal, 0.1 units/kg per meal, or ≈10% of basal dose per meal) rather than continuing basal escalation 1
- Alternatively, add or intensify GLP-1 receptor agonist before advancing to complex insulin regimens 3, 2, 1
Alternative Initial Regimens (Specific Scenarios)
Twice-daily premixed insulin (70/30 NPH/regular or analog premixes):
- Start at 6–10 units twice daily before breakfast and dinner 1
- Consider for patients with predominantly postprandial hyperglycemia 1
- Offers less flexibility than basal insulin but may suit specific patient preferences 7
Basal insulin + GLP-1 receptor agonist combination:
- Reduces weight gain and hypoglycemia risk versus insulin alone 7, 3
- Fixed-ratio combinations available (insulin glargine + lixisenatide; insulin degludec + liraglutide) 7, 2
- Should be considered before adding prandial insulin in patients not at goal on basal insulin alone 2
Once-weekly basal insulin (icodec):
- Approved option providing similar efficacy to daily basal insulin 9
- Reduces injection frequency, potentially improving adherence 9
- Reaches steady state in 3–4 weeks (or 2–3 weeks with 50% loading dose) 9
Intensification Beyond Basal Insulin
If HbA1c remains above target after 3–6 months on optimized basal insulin:
- First option: Add single injection of rapid-acting insulin before largest meal 7
- Second option: Add or switch to GLP-1 receptor agonist (if not already using) 7, 3
- Third option: Advance to basal-bolus regimen with 2+ prandial injections 7
For basal-bolus regimens:
- Use rapid-acting insulin analogs (lispro, aspart, glulisine) over regular human insulin for more physiologic profiles and lower hypoglycemia risk 2
- Ultra-rapid formulations (faster aspart, lispro aabc) allow closer meal-time dosing 2
Special Considerations for Comorbidities
In patients with heart failure (HFrEF or HFpEF):
- Prioritize SGLT2 inhibitor before or alongside insulin for HF hospitalization prevention 6
In patients with CKD (eGFR 20–60 mL/min/1.73m² or albuminuria):
- Use SGLT2 inhibitor for renal protection, though glycemic benefit diminishes at eGFR <45 6
- In advanced CKD (eGFR <30), prefer GLP-1 RA for lower hypoglycemia risk 6
In patients with obesity:
- Strongly consider GLP-1 RA before insulin to address both glycemic and weight goals 6
Monitoring and Follow-Up
Assess quarterly or more frequently:
- Medication adherence and safety 2
- Glycemic control via HbA1c and glucose monitoring patterns 2
- Hypoglycemia frequency and severity 1
De-intensify therapy when: