What would be the Lantus (insulin glargine) dose and carb coverage with U100 for a patient currently using U200 in an ambulatory pump with a basal need of 19.6 units per day and a 1 unit per 10 grams of carbohydrates ratio?

Converting U200 Pump Therapy to U100 Lantus with Carbohydrate Coverage

For a patient on U200 in an ambulatory pump with 19.6 units/day basal needs and 1:10 carb ratio, start Lantus U100 at 10 units once daily (approximately 50% of pump basal) and maintain the 1:10 carb ratio using rapid-acting insulin at meals.

Understanding the Conversion Principles

The key issue here is that U200 and U100 insulin have identical biological effects per unit—only the concentration differs 1. When converting from pump to injections, you're not converting between concentrations but rather transitioning from continuous subcutaneous insulin infusion to multiple daily injections.

Basal Insulin Conversion

The pump basal rate of 19.6 units/day represents approximately 50% of this patient's total daily insulin requirement, suggesting a total daily dose (TDD) of approximately 39 units 2, 3. However, when transitioning from pump to Lantus:

• Start conservatively with 10 units of Lantus U100 once daily (approximately 50% of the pump basal dose), as recommended by the American Diabetes Association for insulin initiation 3
• This conservative approach prevents hypoglycemia during the transition period, as Lantus may provide more consistent absorption than anticipated 3
• Titrate upward by 2-4 units every 3 days based on fasting glucose readings until reaching target of 80-130 mg/dL 3

Why Not Simply Use 19.6 Units?

Pump basal rates often require adjustment when converting to injected basal insulin because:

• Pump therapy provides micro-boluses throughout the day with precise timing 2
• Lantus provides a relatively peakless 24-hour profile but may have slightly different pharmacodynamics 4, 5
• Starting lower (50% of pump basal) allows safe upward titration rather than risking hypoglycemia 3

Carbohydrate Coverage with U100

The carbohydrate-to-insulin ratio of 1:10 remains unchanged when switching from U200 to U100 2. This ratio means:

• For every 10 grams of carbohydrate, administer 1 unit of rapid-acting insulin (Humalog, Novolog, or Apidra) 2
• The ratio is based on insulin sensitivity, not concentration 2
• Use U100 rapid-acting insulin at mealtimes, administered 0-15 minutes before eating 3

Calculating Prandial Doses

If the patient's TDD on pump was approximately 39 units (19.6 basal + ~19.4 bolus):

• Start with approximately 6-7 units of rapid-acting insulin divided among three meals (roughly 50% of TDD as prandial) 3
• Adjust each meal's dose based on carbohydrate intake using the 1:10 ratio 2
• For example: 60g carbs at breakfast = 6 units rapid-acting insulin 2

Practical Implementation Algorithm

Step 1: Initial Dosing

• Lantus U100: 10 units once daily at the same time each day 3
• Rapid-acting insulin U100: Use 1:10 ratio before each meal 2, 3

Step 2: Monitoring During Transition

• Check blood glucose at least 4 times daily (fasting, before meals) during the adjustment period 1
• Monitor for unexpected glycemic patterns, particularly nocturnal hypoglycemia 4, 5

Step 3: Titration Schedule

• Increase Lantus by 2 units every 3 days if fasting glucose is 140-179 mg/dL 3
• Increase Lantus by 4 units every 3 days if fasting glucose ≥180 mg/dL 3
• Decrease Lantus by 2 units if more than 2 fasting values per week are <80 mg/dL 3

Step 4: Recognizing When to Stop Escalating Basal

• When Lantus exceeds 0.5 units/kg/day (approximately 25-30 units for a 50kg patient), consider adding or intensifying prandial insulin rather than continuing to escalate basal alone 3
• Watch for signs of "overbasalization": bedtime-to-morning glucose differential ≥50 mg/dL, hypoglycemia, high glucose variability 3

Critical Pitfalls to Avoid

Concentration Confusion

• Do not adjust the number of units when switching from U200 to U100—the biological effect per unit is identical 1
• The patient will inject a larger volume with U100, but the same number of units 1

Inadequate Prandial Coverage

• Do not rely solely on basal insulin to control postprandial glucose 2, 3
• Lantus addresses fasting and between-meal glucose; rapid-acting insulin is essential for meal coverage 2, 3

Delayed Titration

• Do not wait longer than 3 days between basal insulin adjustments in stable patients, as this unnecessarily prolongs time to glycemic targets 3
• Daily fasting blood glucose monitoring is essential during titration 3

Missing the Foundation

• Continue metformin unless contraindicated when intensifying insulin therapy 3
• Metformin reduces total insulin requirements and provides complementary glucose-lowering effects 3

Special Considerations

If Lantus Doesn't Last 24 Hours

• Consider twice-daily dosing if the patient experiences pre-dinner hyperglycemia despite adequate fasting control 6
• Split the total daily Lantus dose into two injections (e.g., 10 units becomes 5 units twice daily) 6

Patient Education Requirements

• Proper injection technique and site rotation to ensure consistent absorption 3
• Recognition and treatment of hypoglycemia, particularly during the transition period 3
• Self-monitoring of blood glucose with clear targets and action plans 3