How should I write a sliding‑scale prescription for insulin lispro (Humalog) for an inpatient with type 1 or type 2 diabetes and hyperglycemia requiring mealtime coverage?

How to Write a Sliding‑Scale Insulin Lispro (Humalog) Prescription

Sliding‑scale insulin as monotherapy is explicitly condemned by all major diabetes guidelines and should never be prescribed as the sole insulin regimen. 1 Instead, correction doses of insulin lispro must supplement a scheduled basal‑bolus regimen, not replace it. 1

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Why Sliding‑Scale Monotherapy Is Unsafe

• Only ≈38 % of hospitalized patients managed with sliding‑scale insulin alone achieve mean glucose < 140 mg/dL, versus ≈68 % with a scheduled basal‑bolus regimen. 1
• Sliding‑scale insulin reacts to hyperglycemia after it occurs rather than preventing it, leading to dangerous glucose fluctuations and worse clinical outcomes. 1, 2
• The American Diabetes Association and other guideline societies explicitly state that sliding‑scale insulin should never be used as the sole treatment. 1

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Proper Role of Correction (Sliding‑Scale) Insulin Lispro

• Correction insulin must always supplement scheduled basal and prandial insulin—it is never a replacement. 1, 3
• Use correction doses only when pre‑meal glucose exceeds predefined thresholds, in addition to the scheduled prandial dose. 1

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Recommended Correction‑Dose Protocol

Simplified Sliding Scale (Adjunct to Basal‑Bolus)

• Pre‑meal glucose > 250 mg/dL: add 2 units of insulin lispro. 1, 3
• Pre‑meal glucose > 350 mg/dL: add 4 units of insulin lispro. 1, 3

Individualized Correction Using Insulin Sensitivity Factor (ISF)

• Calculate ISF = 1500 ÷ total daily insulin dose. 1
• Correction dose = (Current glucose – Target glucose) ÷ ISF. 1
• Example: If total daily dose is 50 units, ISF = 1500 ÷ 50 = 30. For a glucose of 280 mg/dL with a target of 130 mg/dL, correction dose = (280 – 130) ÷ 30 = 5 units. 1

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Essential Components of a Complete Insulin Regimen

Basal Insulin (Long‑Acting)

• Provide ≈50 % of total daily dose as basal insulin (glargine, detemir, or degludec) once daily. 1, 2
• Basal insulin suppresses hepatic glucose production and prevents fasting hyperglycemia. 1, 2

Prandial Insulin (Rapid‑Acting Lispro)

• Allocate the remaining ≈50 % of total daily dose to prandial insulin, divided among three meals. 1
• Administer insulin lispro 0–15 minutes before meals (ideally immediately before eating) for optimal post‑prandial control. 1, 4, 5, 2
• In hyperglycemic patients, injecting lispro 15 minutes before the meal significantly reduces post‑prandial glucose excursion compared with injection at mealtime. 4

Correction Insulin (Lispro)

• Add correction doses as outlined above when pre‑meal glucose exceeds thresholds. 1, 3

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Initial Dosing for Basal‑Bolus Therapy

Standard‑Risk Patients

• Start with 0.3–0.5 U/kg/day total insulin, split 50 % basal and 50 % prandial. 1
• Example: For a 70‑kg patient, total dose = 21–35 U/day → ≈11–18 U basal once daily + ≈11–18 U prandial (≈4–6 U per meal). 1

High‑Risk Patients (Age > 65, Renal Impairment, Poor Intake)

• Use a lower starting dose of 0.1–0.25 U/kg/day to minimize hypoglycemia risk. 1

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Titration Protocols

Basal Insulin

• Increase by 2 U every 3 days if fasting glucose is 140–179 mg/dL. 1
• Increase by 4 U every 3 days if fasting glucose is ≥180 mg/dL. 1
• Target fasting glucose 80–130 mg/dL. 1

Prandial Lispro

• Increase each meal dose by 1–2 U (≈10–15 %) every 3 days based on 2‑hour post‑prandial glucose. 1
• Target post‑prandial glucose < 180 mg/dL. 1

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Monitoring Requirements

• Patients eating regular meals: check glucose before each meal and at bedtime (minimum 4 times daily). 1, 2
• Patients with poor intake or NPO: check glucose every 4–6 hours. 1
• Use daily fasting glucose to guide basal adjustments. 1
• Obtain 2‑hour post‑prandial glucose after each meal to assess prandial adequacy. 1

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Safety Considerations

Hypoglycemia Management

• Treat glucose < 70 mg/dL immediately with 15 g fast‑acting carbohydrate, recheck in 15 minutes, repeat if needed. 1
• If hypoglycemia occurs without an obvious cause, reduce the implicated insulin dose by 10–20 % promptly. 1

Timing Restrictions

• Never administer insulin lispro at bedtime as a sole correction dose, as this markedly raises nocturnal hypoglycemia risk. 1, 2

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Sample Prescription Format

Insulin Lispro (Humalog) 100 U/mL
Indication: Type 1 or type 2 diabetes requiring mealtime insulin coverage

Dosing Regimen:

1. Prandial (scheduled): [X] units subcutaneously 0–15 minutes before breakfast, lunch, and dinner
2. Correction (sliding scale):
   • Pre‑meal glucose > 250 mg/dL: add 2 units
   • Pre‑meal glucose > 350 mg/dL: add 4 units
   • Administer correction dose in addition to scheduled prandial dose

Basal Insulin (must be prescribed concurrently):
[Specify basal insulin type, dose, and timing]

Monitoring:

• Check capillary glucose before each meal and at bedtime
• Titrate prandial doses by 1–2 units every 3 days based on 2‑hour post‑prandial glucose

Quantity: [Sufficient supply for prescribed duration]
Refills: [As appropriate]

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Common Pitfalls to Avoid

• Do not prescribe sliding‑scale insulin as monotherapy; it is inferior and unsafe. 1, 2
• Do not delay adding prandial insulin when basal insulin alone fails to achieve targets. 1
• Do not rely solely on correction doses without adjusting scheduled basal and prandial insulin. 1
• Do not administer lispro at bedtime as a sole correction dose. 1, 2

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Expected Clinical Outcomes

• With properly implemented basal‑bolus therapy using lispro, ≈68 % of patients achieve mean glucose < 140 mg/dL versus ≈38 % with sliding‑scale alone. 1
• Insulin lispro provides superior post‑prandial glycemic control compared with regular human insulin, with a lower incidence of hypoglycemia. 5, 6
• In elderly type 2 diabetic patients, lispro administered immediately after meals (based on carbohydrate intake) significantly reduces hypoglycemic and hyperglycemic episodes compared with regular insulin given 30 minutes before meals. 7