What is the recommended insulin protocol for adult patients with type 1 or type 2 diabetes, including weight‑based outpatient basal‑bolus dosing, inpatient intravenous regular insulin for uncontrolled hyperglycemia or diabetic ketoacidosis, dose adjustments, transition to subcutaneous insulin, and alternative regimens?

Insulin Protocol for Adult Patients with Diabetes

For hospitalized adults with diabetes, implement a scheduled basal-bolus insulin regimen rather than sliding-scale monotherapy, starting with 0.3–0.5 units/kg/day total dose (50% basal, 50% prandial) for most patients, with adjustments every 3 days based on glucose patterns. 1

Outpatient Basal-Bolus Dosing

Type 1 Diabetes

• Start with 0.5 units/kg/day total daily dose (TDD) for metabolically stable patients, with a range of 0.4–1.0 units/kg/day 2, 3
• Divide as 40–50% basal insulin (glargine, detemir, or degludec) given once daily, typically at bedtime 2, 3
• Allocate 50–60% as prandial insulin (lispro, aspart, or glulisine) divided among three meals, administered 0–15 minutes before eating 2, 3
• Higher doses (up to 1.0 units/kg/day or more) are required during puberty, pregnancy, acute illness, or following ketoacidosis presentation 2

Type 2 Diabetes

• For insulin-naive patients, initiate with 10 units once daily OR 0.1–0.2 units/kg/day of basal insulin 2
• Continue metformin (up to 2000–2550 mg daily) unless contraindicated, as this combination reduces insulin requirements and weight gain 2
• For severe hyperglycemia (A1C ≥9%, glucose ≥300–350 mg/dL, or symptomatic/catabolic features), start immediately with 0.3–0.5 units/kg/day using basal-bolus therapy 2

Titration Algorithm

• Basal insulin adjustment:
  • Increase by 2 units every 3 days if fasting glucose 140–179 mg/dL 2
  • Increase by 4 units every 3 days if fasting glucose ≥180 mg/dL 2
  • Target fasting glucose: 80–130 mg/dL 2
• Prandial insulin adjustment:
  • Increase by 1–2 units (or 10–15%) every 3 days based on 2-hour postprandial glucose 2
  • Target postprandial glucose: <180 mg/dL 2
• If hypoglycemia occurs without clear cause, reduce the implicated dose by 10–20% immediately 2

Critical Threshold: When to Add Prandial Insulin

• When basal insulin exceeds 0.5 units/kg/day and approaches 1.0 units/kg/day without achieving A1C goals, add prandial insulin rather than continuing basal escalation 2
• Start prandial insulin with 4 units before the largest meal OR 10% of current basal dose, then titrate 2
• Signs of "overbasalization" include: basal dose >0.5 units/kg/day, bedtime-to-morning glucose differential ≥50 mg/dL, hypoglycemia episodes, and high glucose variability 2

Inpatient Insulin Management

Non-Critical Care Setting

Basal-Bolus Regimen (Preferred)

• For patients eating regular meals, use 0.3–0.5 units/kg/day total dose, divided as 50% basal and 50% prandial insulin 1, 4
• For high-risk patients (elderly >65 years, renal failure, poor oral intake), reduce starting dose to 0.1–0.25 units/kg/day 2
• For patients on high-dose home insulin (≥0.6 units/kg/day), reduce total daily dose by 20% upon admission 2

Basal-Plus-Correction Regimen

• For patients with poor oral intake or NPO status, provide basal insulin plus correction doses only 1
• Monitor glucose every 4–6 hours for NPO patients 2

Correction Insulin Protocol

• Add 2 units of rapid-acting insulin when pre-meal glucose >250 mg/dL 2
• Add 4 units of rapid-acting insulin when pre-meal glucose >350 mg/dL 2
• Never use sliding-scale insulin as monotherapy—only 38% of patients achieve mean glucose <140 mg/dL versus 68% with basal-bolus therapy 2, 5

Critical Care Setting

• Use continuous intravenous insulin infusion with validated written or computerized protocols 1
• Administer using protocols that allow predefined adjustments based on glycemic fluctuations and insulin infusion rates 1

Diabetic Ketoacidosis (DKA) Management

Acute Phase

• Continuous intravenous insulin is the standard of care for critically ill patients with DKA 1
• For uncomplicated mild-to-moderate DKA, subcutaneous rapid-acting insulin analogs combined with aggressive fluid management may be used in emergency departments 1

Transition Protocol

• Administer subcutaneous basal insulin 2–4 hours before discontinuing IV insulin to prevent rebound hyperglycemia and recurrent ketoacidosis 1, 6
• Calculate subcutaneous dose as 60–80% of the 24-hour IV insulin requirement based on the average hourly rate during the final 6–8 hours of stable glycemic control 6
• Consider adding 0.15–0.3 units/kg of basal insulin analog during IV infusion to reduce duration and prevent rebound hyperglycemia 1

Transition from IV to Subcutaneous Insulin

Calculation Method

• Determine average IV insulin rate during the last 6–8 hours of stable glucose control 6
• Multiply hourly rate by 24 to estimate total daily requirement (e.g., 1.5 units/hour × 24 = 36 units/day) 6
• Convert to 60–80% of calculated requirement for subcutaneous dosing (e.g., 36 × 0.7 = 25 units/day) 6
• Divide as 50% basal insulin once daily and 50% prandial insulin split among three meals 6

Timing

• Give first subcutaneous basal insulin dose 2–4 hours before stopping IV infusion 1, 6
• This overlap ensures adequate insulin coverage during transition 6

Special Populations and Situations

Renal Impairment

• For CKD Stage 5 with type 2 diabetes, reduce total daily dose by 50% 2
• For CKD Stage 5 with type 1 diabetes, reduce total daily dose by 35–40% 2
• Titrate conservatively with eGFR <45 mL/min/1.73 m² to avoid hypoglycemia 2

Perioperative Management

• Reduce basal insulin by 25% the evening before surgery to achieve target glucose with lower hypoglycemia risk 1
• Monitor glucose every 2–4 hours while NPO and dose with short- or rapid-acting insulin as needed 1
• Perioperative glucose target: 80–180 mg/dL 1
• Basal-bolus coverage provides better outcomes than correction-only insulin in noncardiac general surgery 1

Glucocorticoid Therapy

• For patients without diabetes on steroids, consider single morning dose of NPH 2
• For patients with diabetes on steroids, add 0.1–0.3 units/kg/day of glargine to usual regimen, with doses determined by steroid dose and oral intake 2
• Increase prandial and correction insulin by 40–60% or more in addition to basal insulin 2

Enteral/Parenteral Nutrition

• Basal insulin needs are typically 30–50% of total daily insulin requirement 2
• Reasonable starting point: 5 units of NPH/detemir every 12 hours OR 10 units of glargine every 24 hours 2
• For continuous tube feedings, use premixed 70/30 insulin every 8 hours with the same 24-hour total dose (0.6–1.0 units/kg) 4

Monitoring and Hypoglycemia Management

Glucose Monitoring

• Check point-of-care glucose before each meal and at bedtime for patients eating regular meals 2
• Check every 4–6 hours for patients with poor oral intake or NPO 2
• Daily fasting glucose monitoring is essential during outpatient titration 2

Hypoglycemia Protocol

• Treat glucose <70 mg/dL immediately with 15 grams of fast-acting carbohydrate 2
• Recheck in 15 minutes and repeat if needed 2
• Document all episodes in the electronic health record for quality tracking 1
• Review and modify treatment plans when glucose <70 mg/dL is documented 1

Critical Pitfalls to Avoid

• Never use sliding-scale insulin as monotherapy—it leads to dangerous glucose fluctuations and is condemned by all major guidelines 1, 2, 5
• Never give rapid-acting insulin at bedtime as a sole correction dose—this markedly increases nocturnal hypoglycemia risk 2
• Never continue escalating basal insulin beyond 0.5–1.0 units/kg/day without adding prandial coverage—this causes overbasalization with increased hypoglycemia 2
• Never discontinue metformin when starting insulin unless contraindicated—this leads to higher insulin requirements and more weight gain 2
• Never delay insulin initiation in patients not achieving glycemic goals with oral medications—this prolongs hyperglycemia exposure 2
• Never stop an insulin pump without prior subcutaneous basal insulin—this creates a dangerous gap that can precipitate DKA in type 1 diabetes 7
• Never use premixed insulin in hospitalized patients—randomized trials show significantly increased hypoglycemia rates versus basal-bolus regimens 2
• Never dilute or mix Lantus (glargine) with other insulins due to its low pH 2

Alternative Regimens

GLP-1 Receptor Agonist + Basal Insulin

• Consider adding GLP-1 RA to basal insulin when A1C remains above target despite optimized basal dosing 2
• This combination provides comparable or better A1C reduction with lower hypoglycemia risk and weight loss rather than weight gain 2
• Preferred injectable medication before advancing to prandial insulin 2

Basal-Plus Strategy

• Add prandial insulin to one meal (the meal causing greatest postprandial excursion) before advancing to full basal-bolus 8
• Start with 4 units before the largest meal, then add to additional meals as needed based on glucose patterns 2