After a rapid‑acting insulin (lispro) overdose, with a random blood glucose of 155 mg/dL measured 5 hours post‑overdose, when should the next glucose check be performed?

Glucose Monitoring After Rapid-Acting Insulin Overdose

Immediate Next Glucose Check: 1–2 Hours

For a patient 5 hours post–rapid-acting insulin (lispro) overdose with a current glucose of 155 mg/dL, repeat the glucose check in 1–2 hours. 1, 2

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Rationale and Clinical Context

Pharmacokinetics of Lispro Overdose

• Lispro has a peak action at 1–3 hours and a duration of 3–5 hours under normal dosing, but massive overdoses prolong hypoglycemic effects well beyond the expected timeframe 3, 4
• In documented overdose cases, hypoglycemia recurred up to 11 hours after lispro injection, with some patients requiring glucose supplementation for 48–96 hours or longer 3, 4, 5
• A glucose of 155 mg/dL at 5 hours post-overdose does not guarantee stability—the patient remains at high risk for recurrent hypoglycemia as residual subcutaneous insulin continues to be absorbed 3, 4

Evidence from Overdose Case Series

• In a systematic review of 45 insulin overdose cases, 73% experienced intermittent cerebral impairment from recurrent hypoglycemia, and median hospitalization lasted 94 hours (range 12–721 hours) 4
• One case report documented a patient with 300 units of lispro who had three episodes of symptomatic hypoglycemia requiring 50% dextrose boluses, with the last episode occurring 11 hours post-injection 3
• Another case involving 800 units lispro + 3800 units glargine required continuous 10% dextrose for 48 hours, with supplemental dextrose needed on five occasions for glucose <70 mg/dL 6

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Monitoring Protocol for Lispro Overdose

Frequency of Glucose Checks

• Every 1–2 hours until glucose and dextrose infusion rates are stable, then every 4 hours thereafter 1, 2
• Continue hourly checks if the patient is receiving IV dextrose infusion or has had any glucose <70 mg/dL in the preceding 4 hours 1, 6

Duration of Monitoring

• Minimum 24 hours of observation for any insulin overdose, but 48–96 hours or longer is often required for massive overdoses or long-acting formulations 4, 5
• Do not discharge until glucose remains stable >100 mg/dL for at least 12–24 hours without IV dextrose support 4, 5

Target Glucose Range

• Maintain glucose 150–250 mg/dL during the acute management phase to provide a safety buffer against sudden drops 2
• Avoid glucose <70 mg/dL, which requires immediate treatment with 15 g fast-acting carbohydrate or IV dextrose 1

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Treatment Adjustments Based on Glucose Trends

If Glucose Drops Below 150 mg/dL

• Increase dextrose infusion rate by 0.5–1 unit/hour (e.g., from 100 mL/h to 150 mL/h of 10% dextrose) 2, 6
• Recheck glucose in 30–60 minutes after adjustment 2

If Glucose Falls Below 70 mg/dL

• Administer 15 g fast-acting carbohydrate orally if the patient is conscious, or 50 mL of 50% dextrose IV bolus if altered mental status 1, 3
• Recheck glucose 15 minutes after treatment and repeat if still <70 mg/dL 1
• Increase basal dextrose infusion to prevent recurrence 2, 6

If Glucose Exceeds 250 mg/dL

• Decrease dextrose infusion rate by 0.5–1 unit/hour 2
• Recheck glucose in 1–2 hours 2

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Additional Monitoring Requirements

Electrolyte Surveillance

• Check serum potassium every 4–6 hours initially, as insulin drives potassium intracellularly and can cause life-threatening hypokalemia 2, 7, 4
• Monitor for other electrolyte disturbances (42% incidence in overdose cases), including hypomagnesemia and hypophosphatemia 4

Hepatic and Cardiac Function

• Obtain liver function tests at baseline and daily, as 7% of overdose cases develop hepatic disturbances 4
• Perform continuous cardiac monitoring or serial ECGs, as 9% of cases experience cardiac arrhythmias related to electrolyte shifts 4

Neurological Assessment

• Perform frequent neurological checks (every 1–2 hours), as 73% of overdose patients experience intermittent cerebral impairment from recurrent hypoglycemia 4
• Any change in mental status warrants immediate glucose check and treatment 3, 4

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Critical Pitfalls to Avoid

• Do not assume stability based on a single normal glucose reading—recurrent hypoglycemia is the rule, not the exception, in insulin overdose 3, 4
• Do not discontinue dextrose infusion prematurely; taper gradually only after 24–48 hours of stable euglycemia 6, 4, 5
• Do not delay treatment of glucose <70 mg/dL—even brief hypoglycemia can cause permanent neurological damage 4
• Never rely on symptoms alone to detect hypoglycemia, as repeated episodes cause hypoglycemia unawareness 1, 4

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Disposition and Follow-Up

• Admit to intensive care unit for any massive overdose (>300 units) or if glucose has dropped below 70 mg/dL at any point 4
• Psychiatric evaluation is mandatory before discharge for intentional overdoses 6, 4
• Ensure 24-hour observation minimum, with most cases requiring 48–96 hours of hospitalization 4, 5