How and when should regular insulin be prescribed?

How and When to Prescribe Regular Insulin

Regular insulin should be prescribed as prandial (mealtime) coverage given subcutaneously 30 minutes before meals, or as correctional insulin every 4-6 hours for hyperglycemia, with specific dosing based on carbohydrate intake (1 unit per 10-15 grams) or blood glucose thresholds. 1

Clinical Contexts for Regular Insulin Use

Prandial (Mealtime) Insulin

• Administer 30 minutes before meals to align insulin action with postprandial glucose peaks 1
• Starting dose: 1 unit per 10-15 grams of carbohydrate in the meal 1
• Regular insulin is classified as a short-acting prandial insulin alongside rapid-acting analogs (lispro, aspart, glulisine) 1
• Critical timing rule: Do not use regular or rapid-acting insulin at bedtime due to hypoglycemia risk 1

Correctional (Sliding Scale) Insulin

• Administer every 6 hours subcutaneously for hyperglycemia management 1
• Simplified dosing thresholds:
  • For premeal glucose >250 mg/dL (>13.9 mmol/L): give 2 units 1
  • For premeal glucose >350 mg/dL (>19.4 mmol/L): give 4 units 1
• Stop sliding scale when not needed daily to avoid perpetuating reactive rather than proactive management 1

Common pitfall: Sliding-scale insulin alone is ineffective and associated with poor glycemic control in 51-68% of hospitalized patients, with therapeutic benefit in only 12% of administrations 2. Always combine with basal insulin for sustained control.

Hospital-Specific Indications

Enteral Nutrition

• Continuous tube feedings: Give regular insulin every 6 hours subcutaneously, starting with 1 unit per 10-15 grams of carbohydrate per day 1
• Bolus feedings: Administer regular insulin before each feeding at 1 unit per 10-15 grams of carbohydrate 1

Parenteral Nutrition

• Add regular insulin directly to TPN solution if >20 units of correctional insulin required in past 24 hours 1
• Starting dose: 1 unit per 10 grams of dextrose in the solution, adjusted daily 1
• Continue subcutaneous correctional regular insulin every 6 hours as needed 1

Diabetic Ketoacidosis (DKA)

• Mild DKA can be treated with subcutaneous regular insulin rather than IV insulin 1
• Initial priming dose: 0.4-0.6 units/kg body weight, half IV bolus and half subcutaneous/intramuscular 1
• Maintenance: 0.1 unit/kg subcutaneously or intramuscularly every hour until resolution 1
• Resolution criteria: glucose <200 mg/dL, bicarbonate ≥18 mEq/L, venous pH ≥7.3 1

Critical transition: Continue IV insulin for 1-2 hours after starting subcutaneous regimen to prevent rebound hyperglycemia 1

Beta-Blocker Overdose

• High-dose regular insulin with dextrose for refractory shock 1
• Bolus: 1 unit/kg IV, accompanied by 0.5 g/kg dextrose 1
• Infusion: 0.5-1 unit/kg per hour with 0.5 g/kg per hour dextrose, titrated to hemodynamic response 1
• Monitor glucose every 15 minutes initially; target 100-250 mg/dL (5.5-14 mmol/L) 1

Older Adults: Simplification Strategies

When to Reduce or Discontinue Prandial Regular Insulin

• If mealtime insulin ≤10 units/dose: Discontinue prandial insulin and add noninsulin agents 1
• If prandial insulin >10 units/dose: Decrease dose by 50% and add noninsulin agents, with goal to eventually discontinue 1
• This approach reduces hypoglycemia and disease-related distress without worsening glycemic outcomes 1

Target Adjustments

• Premeal glucose goal: 90-150 mg/dL (5.0-8.3 mmol/L) 1
• Adjust goals based on overall health status and life expectancy 1
• If >2 premeal values/week <90 mg/dL: Decrease medication dose 1

Dosing Algorithms for Insulin-Naive Patients

Type 2 Diabetes Starting Insulin

• Begin with basal insulin only (not regular insulin initially) 1
• Regular insulin added later as prandial coverage when basal insulin alone insufficient 1
• Starting prandial dose: 4 units before largest meal or 10% of basal dose, adjusted by 1-2 units every 3 days 1

Perioperative Management

• Day of surgery: Give half of NPH dose or 60-80% of long-acting analog dose 1
• Monitor blood glucose every 4-6 hours while NPO 1
• Dose with short-acting regular insulin as needed for hyperglycemia 1
• Basal-bolus regimen (basal insulin plus premeal regular insulin) superior to sliding scale alone for reducing perioperative complications 1

Key Contraindications and Precautions

• Never administer regular insulin intravenously at subcutaneous doses—this causes severe hypoglycemia due to faster absorption 3
• Do not mix regular insulin with other insulin preparations when using insulin detemir or other specific formulations 3
• Rotate injection sites within same region (thigh, abdomen, upper arm) to prevent lipodystrophy and absorption delays 3
• Temporarily discontinue in acute illness compromising renal or liver function 1

Monitoring Requirements

• Frequent glucose monitoring essential during initiation and dose adjustments 1
• Every 2 weeks: Adjust insulin dose based on premeal finger-stick values 1
• If 50% of premeal values above goal over 2 weeks: Increase dose or add another agent 1
• Patient education on self-titration improves glycemic control significantly 1