How do I adjust basal (long-acting) and prandial (fast-acting) insulin doses for a patient with impaired glucose control?

Adjusting Basal and Prandial Insulin for Impaired Glucose Control

Increase basal insulin by 2-4 units every 3 days until fasting glucose reaches 80-130 mg/dL, but stop escalating when the dose exceeds 0.5 units/kg/day and instead add prandial insulin starting with 4 units before the largest meal. 1

Basal Insulin Titration Algorithm

Start with aggressive basal insulin adjustment:

• If fasting glucose is ≥180 mg/dL: Increase basal insulin by 4 units every 3 days 1
• If fasting glucose is 140-179 mg/dL: Increase basal insulin by 2 units every 3 days 1
• Continue titration until fasting plasma glucose consistently reaches 80-130 mg/dL 1
• If hypoglycemia occurs without clear cause, immediately reduce the dose by 10-20% 1, 2

Daily fasting blood glucose monitoring is essential during the titration phase. 1

Critical Threshold: Recognizing When to Stop Escalating Basal Insulin

When basal insulin exceeds 0.5 units/kg/day and approaches 1.0 units/kg/day, you must add prandial insulin rather than continuing to escalate basal insulin alone. 1, 2 Continuing to increase basal insulin beyond this threshold leads to "overbasalization"—a dangerous pattern that causes increased hypoglycemia risk and suboptimal control without meaningful glycemic improvement. 1

Clinical Signs of Overbasalization:

• Basal insulin dose >0.5 units/kg/day 1
• Bedtime-to-morning glucose differential ≥50 mg/dL 1
• Hypoglycemia episodes 1
• High glucose variability 1

Adding Prandial Insulin Coverage

When to add prandial insulin:

• After 3-6 months of basal insulin optimization, if fasting glucose reaches target but HbA1c remains above goal 1
• When basal insulin approaches 0.5-1.0 units/kg/day without achieving HbA1c targets 1
• When significant postprandial glucose excursions occur (>180 mg/dL) 1

How to initiate prandial insulin:

1. Start with 4 units of rapid-acting insulin before the largest meal (or use 10% of the current basal dose) 1, 3
2. Add prandial insulin before the meal causing the greatest postprandial glucose excursion 1
3. Titrate prandial insulin by 1-2 units or 10-15% every 3 days based on 2-hour postprandial glucose readings 1
4. Gradually add prandial insulin to other meals as needed when postprandial glucose remains >180 mg/dL 4

Rapid-acting insulin analogs (lispro, aspart, glulisine) must be given 0-15 minutes before meals, not after eating. 1, 5

Correction Insulin Dosing

While adjusting prandial insulin, use this simplified correction strategy:

• For premeal glucose >250 mg/dL: Give 2 units of rapid-acting insulin 3
• For premeal glucose >350 mg/dL: Give 4 units of rapid-acting insulin 3
• Do not use rapid-acting insulin at bedtime for routine correction to avoid nocturnal hypoglycemia 3
• Stop the sliding scale when it is not needed daily, as this indicates better baseline control 3

Foundation Therapy Considerations

Continue metformin unless contraindicated, even when adding or intensifying insulin therapy. 1 Metformin reduces total insulin requirements and provides complementary glucose-lowering effects. 1 The maximum effective dose is up to 2500 mg/day, with at least 1000 mg twice daily recommended. 1

Consider adding a GLP-1 receptor agonist to basal insulin to address postprandial hyperglycemia while minimizing weight gain and hypoglycemia risk, particularly when basal insulin exceeds 0.5 units/kg/day. 1, 2

Common Pitfalls to Avoid

• Never continue escalating basal insulin beyond 0.5-1.0 units/kg/day without addressing postprandial hyperglycemia—this leads to overbasalization with increased hypoglycemia and suboptimal control 1
• Do not delay adding prandial insulin when signs of overbasalization are present 1
• Avoid relying solely on sliding scale (correction) insulin without scheduled basal and prandial coverage—this approach is explicitly condemned by all major diabetes guidelines 1
• Do not abruptly discontinue oral medications when starting insulin therapy due to rebound hyperglycemia risk 5
• Never dilute or mix insulin glargine with any other insulin or solution due to its low pH 6

Monitoring Requirements

• Daily fasting blood glucose monitoring during titration 1, 2
• Check pre-meal and 2-hour postprandial glucose to guide prandial insulin adjustments 1
• Assess adequacy of insulin dose at every clinical visit, looking specifically for signs of overbasalization 1
• Reassess and modify therapy every 3-6 months once stable to avoid therapeutic inertia 1