What is the initial dosing regimen for a patient starting on immediate-acting (rapid-acting) insulin and long-acting insulin, considering factors such as age, weight, and renal function (Impaired renal function)?

Initial Insulin Dosing Regimen for Immediate-Acting and Long-Acting Insulin

For insulin-naive patients with type 2 diabetes, start with 10 units of long-acting basal insulin (glargine or detemir) once daily, or use weight-based dosing at 0.1-0.2 units/kg/day, and continue metformin unless contraindicated. 1, 2, 3

Starting Basal (Long-Acting) Insulin

Standard Initiation for Type 2 Diabetes

• Begin with 10 units once daily of insulin glargine (Lantus) or insulin detemir (Levemir), administered at the same time each day 1, 2, 3
• Alternatively, use 0.1-0.2 units/kg/day based on body weight and degree of hyperglycemia 1, 2
• For severe hyperglycemia (A1C ≥9%, blood glucose ≥300-350 mg/dL), consider higher starting doses of 0.3-0.5 units/kg/day as total daily insulin, split between basal and prandial components 2, 4
• Inject subcutaneously into the thigh, upper arm, or abdomen, rotating sites to reduce lipodystrophy risk 5

Type 1 Diabetes Requires Different Approach

• Total daily insulin requirement is typically 0.4-1.0 units/kg/day, with 0.5 units/kg/day being standard for metabolically stable patients 2
• Divide as approximately 50% basal insulin (glargine or detemir once or twice daily) and 50% prandial insulin (rapid-acting analog before meals) 2

Adding Immediate-Acting (Rapid-Acting) Insulin

When to Initiate Prandial Coverage

Add rapid-acting insulin when:

• Basal insulin has been optimized (fasting glucose 80-130 mg/dL) but A1C remains above target after 3-6 months 2
• Basal insulin dose approaches 0.5-1.0 units/kg/day without achieving glycemic goals 2
• Severe hyperglycemia at presentation (A1C ≥10-12% with symptomatic/catabolic features) warrants immediate basal-bolus therapy 2

Starting Dose for Rapid-Acting Insulin

• Begin with 4 units of rapid-acting insulin (lispro, aspart, or glulisine) before the largest meal 2
• Alternatively, use 10% of the current basal insulin dose 2
• Administer 0-15 minutes before meals for optimal postprandial control 1, 6, 7
• Rapid-acting analogs have onset within 5-15 minutes, peak at 1-2 hours, and duration of 3-5 hours 7, 8, 9

Titration Algorithms

Basal Insulin Adjustment

• 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 glucose: 80-130 mg/dL 2
• If hypoglycemia occurs: reduce dose by 10-20% immediately 2

Prandial Insulin Adjustment

• Increase by 1-2 units or 10-15% every 3 days based on 2-hour postprandial glucose readings 2
• Target postprandial glucose: <180 mg/dL 2
• Adjust the dose before the meal causing the greatest glucose excursion 2

Special Considerations for Renal Impairment

Patients with impaired renal function require dose modifications:

• CKD Stage 5 with type 2 diabetes: reduce total daily insulin by 50% 2
• CKD Stage 5 with type 1 diabetes: reduce total daily insulin by 35-40% 2
• Use lower starting doses (0.1-0.25 units/kg/day) for high-risk patients including elderly (>65 years), those with renal failure, or poor oral intake 2, 4
• Monitor more frequently for hypoglycemia as insulin clearance decreases with declining kidney function 2

Foundation Therapy Requirements

Continue metformin unless contraindicated:

• Metformin should be maintained at maximum tolerated dose (up to 2000-2550 mg daily) when adding insulin 1, 2
• This combination provides superior glycemic control with reduced insulin requirements and less weight gain 2
• Consider discontinuing sulfonylureas when advancing beyond basal-only insulin to prevent hypoglycemia 2

Critical Threshold: Avoiding Overbasalization

Stop escalating basal insulin when dose exceeds 0.5 units/kg/day:

• Clinical signals of overbasalization include basal dose >0.5 units/kg/day, bedtime-to-morning glucose differential ≥50 mg/dL, hypoglycemia, and high glucose variability 2
• When basal insulin approaches 0.5-1.0 units/kg/day without achieving targets, add prandial insulin rather than continuing to escalate basal insulin alone 2
• Further basal escalation produces diminishing returns with increased hypoglycemia risk 2

Monitoring Requirements

• Daily fasting blood glucose monitoring is essential during titration 2, 3
• Check pre-meal and 2-hour postprandial glucose to guide prandial insulin adjustments 2
• Reassess every 3 days during active titration and every 3-6 months once stable 2
• Equip patients with self-titration algorithms based on self-monitoring to improve glycemic control 1, 3

Common Pitfalls to Avoid

• Never delay insulin initiation in patients not achieving glycemic goals with oral medications, as this prolongs hyperglycemia exposure 2
• Never use sliding scale insulin as monotherapy—it treats hyperglycemia reactively rather than preventing it 2, 4
• Never discontinue metformin when starting insulin unless contraindicated 2
• Never continue escalating basal insulin beyond 0.5-1.0 units/kg/day without addressing postprandial hyperglycemia 2
• Never give rapid-acting insulin at bedtime as this significantly increases nocturnal hypoglycemia risk 2
• Never mix insulin glargine with other insulins due to its low pH diluent 1, 2

Patient Education Essentials

Comprehensive education must include:

• Proper injection technique and site rotation 2
• Recognition and treatment of hypoglycemia (15 grams fast-acting carbohydrate for glucose ≤70 mg/dL) 2
• Self-monitoring of blood glucose 1, 3
• "Sick day" management rules 2
• Insulin storage and handling 2