What is the standard sliding scale for rapid-acting insulin (e.g. aspart or lispro) in a patient with type 1 diabetes mellitus (T1DM)?

Standard Sliding Scale for Rapid-Acting Insulin in Type 1 Diabetes

Sliding scale insulin as monotherapy should never be used in type 1 diabetes—it is explicitly condemned by all major diabetes guidelines and leads to dangerous glucose fluctuations. 1

Why Sliding Scale Monotherapy Fails in Type 1 Diabetes

Traditional sliding-scale insulin regimens are fundamentally flawed because they treat hyperglycemia reactively after it has already occurred, rather than preventing it. 1 This "reactive" approach causes rapid swings in blood glucose levels, worsening both hyperglycemia and hypoglycemia. 1

The critical problem: Sliding scale insulin without basal coverage has been proven ineffective when used as monotherapy in patients with established insulin requirements. 1 One major issue is that the sliding-scale regimen prescribed on admission typically continues unchanged throughout hospitalization, even when control remains poor. 1

The Correct Approach: Basal-Bolus Therapy

Type 1 diabetes requires a scheduled basal-bolus insulin regimen, not sliding scale monotherapy. 2

Total Daily Insulin Requirements

• Standard dosing: 0.4-1.0 units/kg/day total daily insulin 3
• Typical for metabolically stable patients: 0.5 units/kg/day 3
• Distribution: Approximately 50% as basal insulin and 50% as prandial insulin divided among meals 3

Prandial (Mealtime) Insulin Dosing

Rapid-acting insulin analogs (aspart, lispro, glulisine) should be given 0-15 minutes before meals. 2, 4

Dosing is based on two components:

1. Carbohydrate coverage: Using insulin-to-carbohydrate ratio (ICR)

   • Calculate as: 450 ÷ total daily dose 3
   • Common starting ratio: 1 unit per 10-15 grams of carbohydrate 3

2. Correction dose: Using insulin sensitivity factor (ISF)

   • Calculate as: 1500 ÷ total daily dose 3
   • This determines how much 1 unit of insulin lowers blood glucose 3

Correction Insulin as an Adjunct (Not Monotherapy)

When correction doses ARE appropriate: As a supplement to scheduled basal-bolus therapy, not as standalone treatment. 1

Simplified correction scale for preprandial use (as adjunct only):

• Glucose >250 mg/dL: Add 2 units of rapid-acting insulin 3
• Glucose >350 mg/dL: Add 4 units of rapid-acting insulin 3

Target preprandial glucose: 90-150 mg/dL 3

Pharmacokinetics of Rapid-Acting Insulins

All three rapid-acting analogs (lispro, aspart, glulisine) are interchangeable with equivalent action profiles: 5

• Onset: 0.25-0.5 hours (begins within 15 minutes) 5, 4
• Peak: 1-3 hours (30-90 minutes after administration) 5, 4
• Duration: 3-5 hours 5, 4

These analogs provide superior postprandial glucose control compared to regular human insulin, with 12% reduction in hypoglycemia frequency. 5

Critical Pitfalls to Avoid

• Never use sliding scale insulin as monotherapy in type 1 diabetes—this approach is dangerous and ineffective 1, 2
• Never give rapid-acting insulin at bedtime to correct hyperglycemia, as this significantly increases nocturnal hypoglycemia risk 3
• Never delay scheduled basal-bolus therapy in favor of sliding scale adjustments 1
• Avoid "stacking" correction doses—insulin from the previous dose may still be active 3

When Correction Doses Are Frequently Needed

If correction doses are required frequently, increase the appropriate scheduled insulin doses to accommodate the increased insulin needs, rather than continuing to rely on corrections. 1 This indicates inadequate basal or prandial coverage that needs systematic adjustment.

Monitoring Requirements

• Daily self-monitoring of blood glucose is essential, including preprandial and 2-hour postprandial readings 3
• Adjust prandial insulin every 3 days based on postprandial glucose patterns 3
• Recalculate ICR and ISF periodically (every few weeks to months), not daily 3