What short‑acting insulin dose should be given to a patient with a blood glucose of 500 mg/dL?

Immediate Correction Dose for Blood Glucose of 500 mg/dL

For a blood glucose of 500 mg/dL, give 4 units of short-acting insulin immediately as a correction dose, but recognize this patient requires urgent evaluation for diabetic ketoacidosis and transition to a scheduled basal-bolus insulin regimen rather than relying on correction doses alone. 1

Critical Assessment Required

• Check for diabetic ketoacidosis immediately by measuring urine or blood ketones, especially if the patient has type 1 diabetes or is insulin-dependent, or if symptoms such as nausea, vomiting, abdominal pain, or altered mental status are present 1
• A glucose of 500 mg/dL (27.8 mmol/L) warrants ketone measurement regardless of diabetes type 1
• If ketonuria is present or blood ketones ≥0.5 mmol/L, this patient requires treatment for diabetic ketoacidosis with IV insulin infusion at 0.1 units/kg/hour, not subcutaneous correction doses 1

Immediate Correction Dose Protocol

• The standardized correction protocol recommends 2 units of short-acting insulin for pre-meal glucose >250 mg/dL and 4 units for glucose >350 mg/dL 1, 2
• For a glucose of 500 mg/dL, administer 4 units of short-acting insulin immediately 1
• Recheck capillary blood glucose in 1–2 hours after the correction dose 1
• If glucose remains >300 mg/dL after 2 hours, give an additional correction dose and investigate underlying causes 1

Why Correction Doses Alone Are Inadequate

• A blood glucose of 500 mg/dL signals complete failure of the current insulin regimen, not merely a need for correction 1
• Sliding-scale insulin used as monotherapy is condemned by all major diabetes guidelines because it treats hyperglycemia reactively after it occurs rather than preventing it, leading to dangerous glucose fluctuations 1, 2
• Only 38% of patients on sliding-scale alone achieve mean glucose <140 mg/dL, versus 68% with scheduled basal-bolus regimens 1, 2

Transition to Scheduled Basal-Bolus Therapy

• Discontinue sliding-scale insulin as the sole treatment immediately and initiate a basal-bolus regimen 1, 2
• Start basal insulin at 0.3–0.5 units/kg/day for severe hyperglycemia, constituting approximately 50% of the total daily dose 1, 2
• Give the remaining 50% as prandial insulin divided among three meals using rapid-acting or short-acting insulin 1, 2
• For example, a 70 kg patient would receive approximately 21–35 units total daily: 10.5–17.5 units as basal insulin once daily, and 3.5–6 units before each of three meals 1, 2

Monitoring and Titration

• Check fasting glucose daily and increase basal insulin by 4 units every 3 days if fasting glucose remains ≥180 mg/dL, targeting 80–130 mg/dL 1, 2
• Adjust prandial insulin by 1–2 units every 3 days based on 2-hour postprandial glucose readings, targeting <180 mg/dL 1, 2

Critical Pitfalls to Avoid

• Do not rely solely on correction doses when glucose values are consistently >250 mg/dL; scheduled insulin must be established 1, 2
• Do not administer rapid-acting or short-acting insulin at bedtime as a sole correction dose, as this markedly raises nocturnal hypoglycemia risk 1, 2
• Do not assume that a 4-unit correction is adequate long-term management for a glucose of 500 mg/dL; such dosing indicates fundamental under-dosing of the insulin regimen 1, 2