What is the recommended starting dose and administration schedule for regular insulin (short-acting) in a patient requiring insulin therapy?

Regular Insulin (Short-Acting) Dosing and Administration

For mealtime coverage with regular insulin, start with 4 units per meal or 0.1 units/kg per meal, administered 30 minutes before eating to account for its delayed onset of action compared to rapid-acting analogs. 1

Starting Dose Recommendations

Mealtime (Prandial) Insulin Dosing

• Initial dose: 4 units per meal, 0.1 units/kg per meal, or 10% of the basal insulin dose per meal if HbA1c is <8% 1
• Consider reducing basal insulin by the same amount as the starting mealtime dose to prevent hypoglycemia 1
• For patients with HbA1c ≥8%, higher starting doses may be warranted 1

Basal-Bolus Regimen (Hospital Setting)

• Total daily dose: 0.3-0.5 units/kg for insulin-naive patients 1
• Divide total daily dose: 50% as basal insulin (once or twice daily) and 50% as prandial insulin (divided before three meals) 1
• Lower doses (0.1-0.25 units/kg) are reserved for high-risk patients: older adults (>65 years), renal failure, or poor oral intake 1

Patients Already on Insulin

• For patients on home insulin ≥0.6 units/kg/day, reduce total daily dose by 20% during hospitalization to prevent hypoglycemia 1

Administration Timing: Critical Difference from Rapid-Acting Analogs

Regular insulin requires a 30-minute injection-meal interval (IMI) to optimize postprandial glucose control, unlike rapid-acting analogs which can be given immediately before meals 2, 3, 4

Timing Guidelines

• Optimal timing: 30 minutes before meals for regular insulin 2, 3
• This compensates for regular insulin's delayed onset of action compared to rapid-acting analogs 2
• Shorter intervals (5 minutes) show a tendency toward greater 90-minute postprandial glucose excursions 3
• Most diabetologists recommend IMI of 15-30 minutes when prescribing regular insulin 2

Important Caveat

• Never administer regular or rapid-acting insulin at bedtime without food intake 1, 5
• This significantly increases hypoglycemia risk during sleep 1

Dose Titration Strategy

Basal Insulin Adjustment

• Increase by 2 units every 3 days until fasting plasma glucose reaches target without hypoglycemia 5
• Alternative: increase by 10-15% or 2-4 units once or twice weekly 1
• Target fasting glucose: 90-150 mg/dL (5.0-8.3 mmol/L) for most patients 1

Prandial Insulin Adjustment

• Adjust based on premeal glucose values every 2 weeks 1
• If 50% of premeal values exceed goal over 2 weeks, increase the dose 1
• If >2 premeal values/week are <90 mg/dL, decrease the dose 1

Clinical Context and Regimen Selection

Outpatient Type 2 Diabetes

• Start with basal insulin alone (10 units or 0.1-0.2 units/kg daily), typically with continued metformin 1, 6
• Add mealtime insulin only after basal insulin is optimally titrated and HbA1c remains above target 1
• Regular insulin is less preferred than rapid-acting analogs due to timing requirements, but may be more affordable 1

Hospital Setting

• Basal-bolus regimen superior to sliding scale alone for glycemic control and reducing complications (wound infection, pneumonia, bacteremia, renal/respiratory failure) 1
• Sliding scale insulin alone is discouraged and associated with significant hyperglycemia 1
• Exception: Sliding scale may be appropriate for patients without diabetes who have mild stress hyperglycemia 1

Basal-Plus Approach (Alternative for Mild Hyperglycemia)

• Single dose of basal insulin (0.1-0.25 units/kg/day) plus correctional doses before meals or every 6 hours 1
• Preferred for patients with mild hyperglycemia (<200 mg/dL), decreased oral intake, or undergoing surgery 1
• Lower hypoglycemia risk compared to full basal-bolus regimen 1

Hypoglycemia Risk Management

Risk Stratification

• Basal-bolus regimen: 12-30% incidence of mild hypoglycemia in controlled settings 1
• Risk is 4-6 times higher with basal-bolus compared to sliding scale alone 1
• Severe hypoglycemia is low in controlled settings but may be higher in real-world practice 1

Risk Reduction Strategies

• Use lower starting doses (0.1-0.25 units/kg) in high-risk patients 1
• Reduce basal insulin by 10-20% if hypoglycemia occurs 5
• Monitor blood glucose more frequently after initiating or adjusting insulin 5
• For older adults, consider simplifying complex regimens to match self-management abilities 1

Special Populations

Older Adults

• Simplification of insulin regimens reduces hypoglycemia and disease-related distress without worsening glycemic outcomes 1
• Consider changing basal insulin timing from bedtime to morning for easier management 1
• If prandial insulin >10 units/dose, decrease by 50% and add noninsulin agents rather than continuing complex regimens 1

Perioperative Management

• Reduce basal insulin by 25% the evening before surgery to achieve perioperative glucose goals with lower hypoglycemia risk 1
• Basal-bolus coverage improves outcomes compared to correction-only insulin in noncardiac general surgery 1

Common Pitfalls to Avoid

• Do not use sliding scale insulin alone in patients with established diabetes requiring insulin therapy 1
• Do not use premixed insulin (70/30) in the hospital due to unacceptably high hypoglycemia rates 1
• Do not forget the 30-minute injection-meal interval when using regular insulin instead of rapid-acting analogs 2, 3
• Do not continue home insulin doses unchanged during hospitalization—reduce by 20% if ≥0.6 units/kg/day 1