What is the recommended approach for initiating insulin therapy in a patient with diabetes?

Initiating Insulin Therapy in Diabetes

Type 1 Diabetes: Start Basal-Bolus Immediately

For type 1 diabetes, initiate multiple daily injections at diagnosis with a total daily dose of 0.5 units/kg/day, split as 40-60% basal insulin and 40-60% prandial insulin divided before meals. 1, 2

• Begin with basal insulin (NPH, glargine, detemir, or degludec) administered once daily at the same time each day 3, 1
• Add rapid-acting insulin analogue (lispro, aspart, or glulisine) 0-15 minutes before each meal 1, 4
• Long-acting basal analogs (glargine or detemir) reduce nocturnal and level 2 hypoglycemia compared to NPH insulin 3
• Longer-acting analogs (U-300 glargine or degludec) further reduce nocturnal hypoglycemia risk versus U-100 glargine 3

Type 2 Diabetes: Basal Insulin First

For type 2 diabetes, start basal insulin at 10 units once daily (or 0.1-0.2 units/kg/day) while continuing metformin unless contraindicated. 3, 1, 2

When to Start Insulin in Type 2 Diabetes:

• Immediately if A1C ≥10% or blood glucose ≥300-350 mg/dL, especially with symptomatic hyperglycemia or catabolic features 3, 2
• Consider strongly when A1C ≥9% despite optimal oral therapy 3, 2, 4
• Add to regimen when A1C ≥7.5% and oral agents have been optimally used 4

Basal Insulin Titration Protocol:

Titrate aggressively every 3 days based on fasting glucose until target of 80-130 mg/dL is achieved. 1, 2

• If fasting glucose 140-179 mg/dL: increase by 2 units every 3 days 1
• If fasting glucose ≥180 mg/dL: increase by 4 units every 3 days 1
• Alternative: increase by 10-15% of current dose once or twice weekly 2
• Daily fasting glucose monitoring is mandatory during titration 1

When to Add Prandial Insulin

If basal insulin is optimized (fasting glucose at target) but A1C remains above goal, add GLP-1 receptor agonist first before advancing to prandial insulin. 3, 2

Signs of Overbasalization (Stop Increasing Basal):

• Basal dose exceeds 0.5 units/kg 3, 2
• High bedtime-to-morning glucose differential 3, 2
• Frequent hypoglycemia or high glucose variability 2

Adding Prandial Insulin:

• Start with 4 units or 10% of basal insulin dose at the largest meal 3
• Patients with type 2 diabetes typically require higher doses (up to 1 unit/kg total daily) than type 1 diabetes 3
• When adding significant prandial insulin (especially at dinner), reduce basal insulin dose 3

Critical Medication Management

Continue metformin with insulin therapy—it reduces insulin requirements, prevents weight gain, and improves cardiovascular outcomes. 3, 1, 2

• Stop sulfonylureas when advancing beyond basal-only insulin to prevent hypoglycemia 1, 2
• Discontinue DPP-4 inhibitors and GLP-1 receptor agonists when using complex insulin regimens beyond basal insulin 2

Administration Technique

Inject subcutaneously into the abdomen, thigh, or deltoid, rotating injection sites within the same region to prevent lipodystrophy. 1, 5

• Administer basal insulin at the same time every day, any time of day 1, 5
• Give rapid-acting insulin 0-15 minutes before meals 1, 4
• Never administer intravenously or via insulin pump 5
• Do not dilute or mix insulin glargine with any other insulin or solution 5

Essential Patient Education

Provide comprehensive education on self-monitoring, hypoglycemia recognition and treatment, injection technique with site rotation, insulin storage, and "sick day" management. 1, 2

• Teach type 1 diabetes patients to match prandial insulin to carbohydrate intake, premeal glucose, and anticipated activity 2
• Explain that type 2 diabetes is progressive and insulin becomes necessary as beta-cell function declines—not due to patient failure 3, 1, 2
• Equip patients with self-titration algorithms based on fasting glucose monitoring 3, 2

Critical Pitfalls to Avoid

Never use sliding scale insulin as monotherapy—it treats hyperglycemia reactively rather than preventing it. 3, 1

• Do not delay insulin initiation in patients not achieving goals with oral agents—this prolongs hyperglycemia exposure 1, 2
• Do not continue escalating basal insulin beyond 0.5-1.0 units/kg/day without adding prandial coverage—this causes overbasalization with increased hypoglycemia 1
• Do not inject into areas of lipodystrophy or localized cutaneous amyloidosis, as this causes erratic absorption and hyperglycemia 3, 5
• Do not abruptly discontinue oral medications when starting insulin due to risk of rebound hyperglycemia 4

Special Populations

Hospitalized Patients:

• Start at 0.3-0.5 units/kg/day total (50% basal, 50% bolus) for those eating regular meals 1
• Target glucose 140 mg/dL for non-critically ill patients 3
• Target glucose as close to 110 mg/dL as possible for critically ill patients 3

Renal Impairment:

• Reduce total daily dose by 50% for CKD Stage 5 with type 2 diabetes 1
• Reduce by 35-40% for CKD Stage 5 with type 1 diabetes 1
• Titrate conservatively with eGFR <45 mL/min/1.73 m² 1