What should be done if a patient receives 30 units of insulin lispro (rapid‑acting insulin) instead of the prescribed 18 units?

Immediate Management of Insulin Lispro Overdose

If a patient receives 30 units of insulin lispro instead of the prescribed 18 units, immediately provide 15–30 grams of fast-acting carbohydrate and begin continuous glucose monitoring every 15–30 minutes for at least 4–6 hours, as hypoglycemia from rapid-acting insulin overdose can persist for 11 hours or longer. 1

Immediate Actions (First 15 Minutes)

• Administer 15–30 grams of fast-acting carbohydrate immediately if the patient is conscious and able to swallow—examples include 4–6 glucose tablets, 120–240 mL of fruit juice, or 3–6 teaspoons of sugar dissolved in water. 2
• Check capillary blood glucose within 5 minutes of carbohydrate administration to establish a baseline. 2
• Do not wait for symptoms to appear before treating, as the 12-unit excess (67% overdose) will cause significant hypoglycemia within 15–30 minutes given lispro's rapid onset. 3

Monitoring Protocol

• Check blood glucose every 15 minutes for the first hour, then every 30 minutes for hours 2–4, then hourly for hours 5–11 after the injection. 1
• Maintain continuous observation for at least 11 hours after the overdose, as case reports document recurrent severe hypoglycemia (requiring 50% dextrose boluses) occurring up to 11 hours post-injection even with insulin lispro's short duration of action. 1
• Monitor for neurological symptoms including confusion, altered mental status, seizures, or loss of consciousness—any of these warrant immediate intravenous glucose administration. 1

Glucose Replacement Strategy

• If blood glucose falls below 70 mg/dL at any point, immediately give another 15 grams of fast-acting carbohydrate and recheck in 15 minutes. 2
• If blood glucose drops below 54 mg/dL or the patient becomes symptomatic (tremor, sweating, confusion), administer 30 grams of fast-acting carbohydrate and consider intravenous access for potential dextrose infusion. 2
• For recurrent hypoglycemia despite oral carbohydrate, initiate continuous intravenous 10% dextrose infusion at a rate equivalent to maximal glucose disposal (typically 5–10 g/hour or 50–100 mL/hour of D10W). 1

Meal Timing Adjustment

• Do not skip the meal for which the 30 units was intended—the patient must eat the planned meal on schedule to utilize the excess insulin. 4
• Consider adding 15–30 grams of additional carbohydrate to the planned meal to buffer against the 12-unit excess (approximately 1 unit covers 10–15 grams of carbohydrate, so 12 extra units require 120–180 grams additional carbohydrate). 2

Hospital Admission Criteria

• Admit for observation if:
  • Blood glucose falls below 40 mg/dL at any point 1
  • More than two hypoglycemic episodes occur within the first 4 hours 1
  • The patient has altered mental status or seizure activity 1
  • The patient lives alone or lacks reliable supervision for 12-hour monitoring 1
  • The patient has impaired hypoglycemia awareness or a history of severe hypoglycemia 2

Pharmacokinetic Considerations

• Insulin lispro peaks at 1–3 hours and has a duration of 3–5 hours under normal circumstances, but overdose can extend hypoglycemic effects beyond 11 hours due to depot formation at the injection site. 1, 3
• The 12-unit excess represents approximately 40–60 mg/dL additional glucose-lowering effect per hour during the peak action period (assuming insulin sensitivity factor of 30–50 mg/dL per unit). 2
• Plasma insulin levels remain elevated for 18 hours after massive overdose (documented level of 11 mU/L at 18 hours post-injection in a 300-unit overdose case), explaining prolonged hypoglycemia risk. 1

Critical Pitfalls to Avoid

• Do not assume the hypoglycemia risk ends after 3–5 hours based on lispro's labeled duration—case reports document severe hypoglycemia requiring treatment up to 11 hours post-injection. 1
• Do not rely on a single glucose check and carbohydrate dose—recurrent hypoglycemia is the rule rather than the exception in insulin overdose. 1
• Do not use protein or fat to treat hypoglycemia—only pure glucose or fast-acting carbohydrates provide rapid enough correction. 2
• Do not discharge the patient before 12 hours of observation unless glucose has remained stable above 100 mg/dL for at least 4 consecutive hours without additional carbohydrate intervention. 1

Documentation and Follow-Up

• Document the exact time of injection, dose given, and all glucose values with corresponding interventions to guide ongoing management. 2
• Review insulin administration technique with the patient after the acute event to prevent recurrence—common errors include incorrect syringe selection (U-100 vs U-500), misreading pen dial, or double-dosing. 5
• Reduce the next scheduled insulin dose by 10–20% if the overdose occurred close to the next scheduled injection time to avoid cumulative effect. 2