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

How to Give Insulin Therapy

Start with basal insulin at 10 units once daily (or 0.1-0.2 units/kg/day) for type 2 diabetes, or 0.5 units/kg/day split 50% basal/50% prandial for type 1 diabetes, and titrate aggressively every 3 days based on fasting glucose until targets are achieved. 1, 2, 3

Initial Insulin Regimen Selection

Type 2 Diabetes

• Begin with basal insulin alone as the most convenient initial approach for most patients 1, 3
• Administer 10 units once daily OR 0.1-0.2 units/kg body weight at the same time each day 1, 2, 3
• Continue metformin (unless contraindicated) and possibly one additional non-insulin agent 1, 2, 3
• Preferred basal insulins: glargine, detemir, or degludec 3, 4

Exception for severe hyperglycemia: If HbA1c ≥10-12% with symptomatic/catabolic features OR blood glucose ≥300-350 mg/dL, start basal-bolus insulin immediately at 0.3-0.5 units/kg/day total (50% basal, 50% prandial divided among meals) 1, 2, 3

Type 1 Diabetes

• Require basal-bolus therapy from diagnosis 1, 5
• Total daily dose: 0.5 units/kg/day (range 0.4-1.0 units/kg/day) 1, 2
• Split: 40-60% as basal insulin, 40-60% as prandial insulin divided before meals 1, 2
• Must use rapid-acting insulin (lispro, aspart, or glulisine) 0-15 minutes before meals 1, 5

Insulin Administration Technique

Critical Administration Rules

• Inject subcutaneously into abdomen, thigh, or deltoid 6
• Rotate injection sites within the same region to prevent lipodystrophy 6, 5
• Never inject into lipodystrophy areas as this causes erratic absorption and hyperglycemia 6
• Do NOT administer intravenously or via insulin pump for glargine 6
• Do NOT dilute or mix glargine with other insulins 6
• Use 4-mm pen needles or 6-mm syringe needles as first-line to minimize pain and avoid intramuscular injection 5

Timing

• Basal insulin: same time every day, any time of day 1, 6
• Rapid-acting insulin: 0-15 minutes before meals 1, 5
• Never give rapid-acting insulin at bedtime due to nocturnal hypoglycemia risk 1

Aggressive Titration Protocol

Basal Insulin Titration

Target fasting glucose: 80-130 mg/dL 1, 2, 3

• If fasting glucose 140-179 mg/dL: increase by 2 units every 3 days 1, 2
• If fasting glucose ≥180 mg/dL: increase by 4 units every 3 days 1, 2
• If hypoglycemia occurs: reduce dose by 10-20% immediately 1, 2
• If >2 fasting values/week <80 mg/dL: decrease by 2 units 2

Daily fasting glucose monitoring is mandatory during titration 1, 2, 3

When to Add Prandial Insulin

Critical threshold: When basal insulin exceeds 0.5 units/kg/day and approaches 1.0 units/kg/day, stop escalating basal insulin and add prandial coverage 1, 2

Clinical signals of "overbasalization": 2

• Basal dose >0.5 units/kg/day
• Bedtime-to-morning glucose drop ≥50 mg/dL
• Hypoglycemia episodes
• High glucose variability despite adequate fasting glucose

Add prandial insulin when: 1, 2, 3

• Fasting glucose at target (80-130 mg/dL) but HbA1c remains above goal after 3-6 months
• Basal insulin dose approaches 0.5-1.0 units/kg/day without achieving HbA1c target

Prandial Insulin Initiation

• Start with 4 units of rapid-acting insulin before the largest meal OR 10% of basal dose 1, 2
• Titrate by 1-2 units or 10-15% every 3 days based on 2-hour postprandial glucose 1, 2
• Target postprandial glucose: <180 mg/dL 1

Essential Patient Education

Mandatory Teaching Points

• Self-monitoring of blood glucose: check fasting daily during titration 1, 3
• Hypoglycemia recognition and treatment: use 15 grams fast-acting carbohydrate for glucose ≤70 mg/dL 2
• Injection technique and site rotation to prevent lipodystrophy 1, 6, 5
• Insulin storage and handling 1
• "Sick day" management rules 1, 2
• Self-titration algorithms improve glycemic control 1, 3

Progressive Nature of Diabetes

Never use insulin as a threat or punishment 1, 3. Explain that type 2 diabetes is progressive and insulin becomes necessary as beta-cell function declines, not due to patient failure 1

Medication Management with Insulin

Continue These Medications

• Metformin: MUST continue unless contraindicated—reduces insulin requirements, prevents weight gain, improves cardiovascular outcomes 1, 2, 3, 5, 7
• SGLT2 inhibitors or thiazolidinediones: may continue to reduce total insulin dose 1, 3

Discontinue These Medications

• Sulfonylureas: stop when advancing beyond basal-only insulin to prevent hypoglycemia 1, 3
• DPP-4 inhibitors: discontinue with complex insulin regimens 3
• GLP-1 receptor agonists: discontinue if using prandial insulin (unless using fixed-ratio combination) 3

Critical Pitfalls to Avoid

Dangerous Practices

• Sliding scale insulin as monotherapy is condemned by all guidelines—it treats hyperglycemia reactively rather than preventing it 1, 2
• Delaying insulin initiation in patients not achieving goals with oral agents prolongs hyperglycemia exposure 2, 3
• Continuing to escalate basal insulin beyond 0.5-1.0 units/kg/day without adding prandial coverage causes overbasalization with increased hypoglycemia 1, 2
• Stopping metformin when starting insulin leads to higher insulin requirements and more weight gain 2, 3, 7
• Injecting into lipodystrophy areas causes erratic absorption 6, 5

Monitoring Failures

• Not titrating insulin doses within 3 days of initiation delays glycemic control 1, 2
• Failing to recognize overbasalization signs leads to hypoglycemia and poor control 2
• Not checking fasting glucose daily during titration prevents appropriate dose adjustments 1, 2

Special Populations

Hospitalized Patients

• Start 0.3-0.5 units/kg/day total (50% basal, 50% bolus) for those eating regular meals 2
• Reduce home insulin by 20% if ≥0.6 units/kg/day to prevent hypoglycemia 2
• Use lower doses (0.1-0.25 units/kg/day) for elderly >65 years, renal failure, or poor oral intake 2

Renal Impairment

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

Pregnancy and Puberty

• Higher doses often required (may exceed 1.0 units/kg/day) 2