What is the recommended approach for initiating insulin therapy in a patient with type 2 diabetes (T2D) and potentially impaired renal function?

Insulin Initiation in Type 2 Diabetes

For patients with type 2 diabetes requiring insulin therapy, initiate basal insulin at 10 units once daily (or 0.1-0.2 units/kg/day) if renal function is normal, while continuing metformin unless contraindicated. 1, 2

Clinical Decision Algorithm for Insulin Initiation

Assess Disease Severity First

Metabolically Stable Patients (A1C <8.5%, asymptomatic):

• Start metformin as first-line therapy if renal function is normal 1
• Add basal insulin only if glycemic targets are not met after 3 months of optimal oral therapy 1

Marked Hyperglycemia (Blood glucose ≥250 mg/dL or A1C ≥8.5%) without acidosis:

• Initiate basal insulin immediately while starting/titrating metformin 1
• Starting dose: 10 units once daily or 0.1-0.2 units/kg/day 2
• For more severe presentations (A1C ≥9%), consider higher starting doses of 0.3-0.4 units/kg/day 2

Severe Hyperglycemia (Blood glucose ≥300-350 mg/dL or A1C ≥10-12% with symptoms):

• Start basal-bolus insulin regimen immediately (0.3-0.5 units/kg/day total, split 50% basal/50% prandial) 2, 3
• This bypasses the stepwise approach due to severe metabolic decompensation 2

Ketosis/Ketoacidosis:

• Initiate IV or subcutaneous insulin immediately to correct metabolic derangement 1
• Once acidosis resolves, continue subcutaneous insulin while adding metformin 1

Renal Function Considerations

Normal Renal Function:

• Metformin is safe and should be continued with insulin therapy 1, 2
• Standard insulin dosing applies 2

Impaired Renal Function:

• Use lower initial insulin doses (0.1-0.25 units/kg/day) to prevent hypoglycemia 2
• Metformin may be contraindicated depending on degree of impairment 1
• Elderly patients (>65 years) with any degree of renal impairment require the lower dosing range 2

Specific Insulin Initiation Protocol

Starting Dose Calculation

Standard approach for most patients:

• 10 units of long-acting basal insulin (glargine or detemir) once daily at the same time each day 2
• Alternative: 0.1-0.2 units/kg body weight once daily 2

For a 50 kg patient: Start with 10 units once daily 2

For severe hyperglycemia (A1C ≥9%): Consider 0.3-0.4 units/kg/day 2

Titration Algorithm

Increase basal insulin systematically based on fasting glucose:

• If fasting glucose 140-179 mg/dL: increase by 2 units every 3 days 2
• If fasting glucose ≥180 mg/dL: increase by 4 units every 3 days 2
• Target fasting plasma glucose: 80-130 mg/dL 2

If hypoglycemia occurs:

• Determine the cause and reduce dose by 10-20% immediately 2

Critical threshold to recognize:

• 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 2, 3
• This prevents "overbasalization" which causes hypoglycemia and suboptimal control 2

Foundation Therapy Requirements

Metformin must be continued unless contraindicated:

• Reduces total insulin requirements 4
• Provides complementary glucose-lowering effects 2
• Associated with decreased weight gain and less hypoglycemia compared to insulin alone 4

Do not abruptly discontinue oral medications when starting insulin:

• Risk of rebound hyperglycemia 4
• Metformin should be continued even when intensifying insulin therapy 2

Monitoring Requirements

During titration phase:

• Daily fasting blood glucose monitoring is essential 2
• Assess adequacy of insulin dose at every clinical visit 2
• Check A1C every 3 months 1

Look for signs of overbasalization:

• Basal dose >0.5 units/kg/day 2
• Bedtime-to-morning glucose differential ≥50 mg/dL 2
• Hypoglycemia episodes 2
• High glucose variability 2

Common Pitfalls to Avoid

Delaying insulin initiation:

• Do not delay insulin therapy in patients not achieving glycemic goals with oral medications 2
• Prolonged hyperglycemia exposure increases complication risk 2

Continuing to escalate basal insulin beyond appropriate limits:

• Do not increase basal insulin beyond 0.5-1.0 units/kg/day without addressing postprandial hyperglycemia 2
• Blood glucose in the 200s mg/dL reflects both inadequate basal coverage AND postprandial excursions requiring mealtime insulin 2

Ignoring the need for prandial insulin:

• When basal insulin is optimized (fasting glucose 80-130 mg/dL) but A1C remains above target after 3-6 months, add prandial insulin 2
• Start with 4 units of rapid-acting insulin before the largest meal or 10% of current basal dose 2

Abruptly stopping metformin:

• Metformin should be continued when adding or intensifying insulin therapy unless contraindicated 2, 4

Special Populations

Elderly patients (>65 years):

• Use lower starting doses (0.1-0.25 units/kg/day) 2
• Higher risk for hypoglycemia requires more conservative targets 2

Patients with poor oral intake or acute illness:

• Reduce doses to 0.1-0.25 units/kg/day 2
• Monitor closely for hypoglycemia 2

Hospitalized patients on high-dose home insulin (≥0.6 units/kg/day):

• Reduce total daily dose by 20% upon admission to prevent hypoglycemia 2