What is the best approach for adjusting insulin therapy in an adult patient with type 2 diabetes mellitus (T2DM)?

Insulin Adjustment in Adult Type 2 Diabetes

Initial Insulin Therapy

Start basal insulin at 10 units once daily or 0.1-0.2 units/kg body weight, administered at the same time each day, and continue metformin unless contraindicated. 1, 2

• For patients with severe hyperglycemia (blood glucose ≥300-350 mg/dL and/or A1C ≥10-12% with symptomatic or catabolic features), initiate basal-bolus insulin immediately rather than basal insulin alone 1
• For moderate-to-severe hyperglycemia (A1C ≥9%), consider higher starting doses of 0.3-0.4 units/kg/day 1, 2
• Basal insulin options include NPH, insulin glargine, or insulin detemir, with long-acting analogs associated with modestly less overnight hypoglycemia 1

Basal Insulin Titration Algorithm

Equip patients with self-titration algorithms based on self-monitoring of blood glucose, adjusting every 3 days until fasting glucose reaches 80-130 mg/dL. 1, 2

Specific Titration Steps:

• If fasting glucose is 140-179 mg/dL: increase by 2 units every 3 days 1, 2
• If fasting glucose is ≥180 mg/dL: increase by 4 units every 3 days 1, 2
• If >2 fasting glucose values per week are <80 mg/dL: decrease by 2 units 1, 2
• If hypoglycemia occurs without clear cause: reduce dose by 10-20% immediately 1, 2

Critical Threshold for Basal Insulin:

When basal insulin exceeds 0.5 units/kg/day and approaches 1.0 units/kg/day, add prandial insulin rather than continuing to escalate basal insulin alone. 1, 2

• Clinical signals of "overbasalization" include: basal dose >0.5 units/kg/day, bedtime-to-morning glucose differential ≥50 mg/dL, hypoglycemia episodes, and high glucose variability 2
• Continuing to escalate basal insulin beyond this threshold leads to suboptimal control and increased hypoglycemia risk 1, 2

Adding Prandial Insulin

If basal insulin has been titrated to achieve acceptable fasting glucose (80-130 mg/dL) but A1C remains above target after 3-6 months, add prandial insulin coverage. 1, 2

Prandial Insulin Initiation:

• Start with 4 units of rapid-acting insulin (lispro, aspart, or glulisine) before the largest meal 1, 2
• Alternatively, use 10% of the current basal dose 1, 2
• Administer rapid-acting insulin 0-15 minutes before meals 1, 3
• Titrate by 1-2 units or 10-15% every 3 days based on 2-hour postprandial glucose readings 1, 2
• Target postprandial glucose <180 mg/dL 1, 2

Alternative to Prandial Insulin:

• Consider adding a GLP-1 receptor agonist to basal insulin to address postprandial hyperglycemia while minimizing weight gain and hypoglycemia risk 1, 2

Foundation Therapy Considerations

Continue metformin at maximum tolerated dose (up to 2000-2550 mg daily) when adding or intensifying insulin therapy unless contraindicated. 1, 2

• Metformin combined with insulin reduces weight gain, lowers insulin dose requirements, and decreases hypoglycemia compared with insulin alone 1, 3
• Discontinue sulfonylureas when advancing beyond basal-only insulin to prevent hypoglycemia 1
• DPP-4 inhibitors are typically stopped once more complex insulin regimens beyond basal are used 1

Monitoring Requirements

Daily fasting blood glucose monitoring is essential during titration, with dose reassessment every 3 days during active titration and every 3-6 months once stable. 1, 2

• Check pre-meal glucose before each prandial insulin injection 2, 4
• Check 2-hour postprandial glucose to assess adequacy of meal coverage 2, 4
• Assess for signs of overbasalization at every clinical visit 2

Patient Education Essentials

Comprehensive education regarding self-monitoring of blood glucose, insulin injection technique, recognition/treatment of hypoglycemia, and "sick day" rules is imperative. 1

• Treat hypoglycemia (glucose ≤70 mg/dL) immediately with 15 grams of fast-acting carbohydrate 2
• Rotate injection sites within the same region to prevent lipohypertrophy 5, 3
• Continue insulin during illness even if unable to eat or vomiting 1
• Carry medical identification indicating insulin use 1

Common Pitfalls to Avoid

• Never delay insulin initiation in patients not achieving glycemic goals with oral medications, as this prolongs hyperglycemia exposure and increases complication risk 1, 2
• Never discontinue metformin when starting insulin unless contraindicated, as this leads to higher insulin requirements and more weight gain 2
• Never continue escalating basal insulin beyond 0.5-1.0 units/kg/day without addressing postprandial hyperglycemia, as this causes overbasalization 1, 2
• Never use sliding scale insulin as monotherapy, as it treats hyperglycemia reactively rather than preventing it, leading to dangerous glucose fluctuations 2
• Never give rapid-acting insulin at bedtime to avoid nocturnal hypoglycemia risk 1, 2

Special Populations

Older Adults (>65 years):

• Use lower starting doses (0.1-0.25 units/kg/day) for high-risk patients with renal failure or poor oral intake 1, 2
• Consider less stringent A1C targets (7.5-8.0%) based on overall health status and life expectancy 1

Hospitalized Patients:

• For patients on high-dose home insulin (≥0.6 units/kg/day), reduce total daily dose by 20% upon admission to prevent hypoglycemia 2
• Use basal-bolus regimens rather than sliding scale monotherapy 2

Renal Impairment:

• For CKD Stage 5 with type 2 diabetes, reduce total daily insulin dose by 50% 2
• Titrate conservatively in patients with eGFR <45 mL/min/1.73 m² 2