In a 45-year-old man with cellulitis, hyperglycemia 300–320 mg/dL, no prior diabetes, and weight 73 kg, which therapy is most appropriate to initiate in the hospital: intravenous insulin infusion, subcutaneous basal‑bolus insulin with correctional dosing, subcutaneous sliding‑scale insulin, or oral metformin?

Subcutaneous Basal-Bolus Insulin Is the Most Appropriate Therapy

For this 45-year-old hospitalized patient with new hyperglycemia (glucose 300–320 mg/dL) in the setting of cellulitis, initiate subcutaneous basal-bolus insulin with correctional dosing immediately. This regimen provides scheduled basal insulin to suppress hepatic glucose production, prandial insulin to cover meals, and correction doses to address breakthrough hyperglycemia—a physiologic approach that prevents the dangerous glucose fluctuations seen with sliding-scale monotherapy.

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Why Basal-Bolus Insulin Is Superior

• Sliding-scale insulin as monotherapy is explicitly condemned by the American Diabetes Association because it treats hyperglycemia reactively after it occurs rather than preventing it, leading to wide glucose fluctuations and poor outcomes 1.
• Only 38% of patients on sliding-scale alone achieve mean glucose <140 mg/dL, compared with 68% using scheduled basal-bolus therapy, with no increase in hypoglycemia when properly implemented 1, 2, 3.
• Basal-bolus regimens result in significantly lower treatment failure rates (defined as >2 consecutive glucose readings >240 mg/dL) compared with sliding-scale insulin: 0–2% versus 19% 4.

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Why IV Insulin Is Not Indicated

• Continuous IV insulin infusion is reserved for critically ill patients—those who are hemodynamically unstable, on vasopressors, or in diabetic ketoacidosis 5.
• This patient is on a medical floor with cellulitis and stable vital signs; he does not meet criteria for ICU-level care or IV insulin 5.
• IV insulin requires hourly glucose monitoring and ICU-level nursing, which is neither necessary nor practical for this stable patient 5.

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Why Oral Metformin Is Inappropriate

• Metformin is contraindicated in hospitalized patients with acute infection (cellulitis) due to the high risk of lactic acidosis from hypoperfusion, renal insufficiency, and tissue hypoxia 1.
• The most common risk factors for metformin-associated lactic acidosis—cardiac disease, hypoperfusion, renal insufficiency, and acute illness—are substantially elevated in the hospital setting 1.
• Metformin has a delayed onset of action (days to weeks) and provides insufficient glucose-lowering for this degree of hyperglycemia (300–320 mg/dL) 1.

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Specific Basal-Bolus Insulin Dosing for This Patient

Initial Total Daily Dose Calculation

• For a 73-kg patient with glucose 300–320 mg/dL, start with 0.3–0.5 units/kg/day total insulin dose 6, 3.
• This translates to approximately 22–37 units/day total 6.
• Split 50% as basal insulin (glargine or detemir once daily) = 11–18 units 1, 6.
• Split 50% as prandial insulin (lispro, aspart, or glulisine before meals) = 11–18 units total, divided among three meals ≈ 4–6 units per meal 1, 6.

Practical Starting Regimen

• Basal insulin (glargine): 15 units subcutaneously once daily at bedtime 6.
• Prandial insulin (lispro or aspart): 5 units subcutaneously before each of three meals 6.
• Correction insulin: Add 2 units for pre-meal glucose >250 mg/dL; add 4 units for glucose >350 mg/dL 1, 6.

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Titration Protocol

Basal Insulin Adjustment

• Increase by 2 units every 3 days if fasting glucose is 140–179 mg/dL 6.
• Increase by 4 units every 3 days if fasting glucose is ≥180 mg/dL 6.
• Target fasting glucose: 80–130 mg/dL 1, 6.

Prandial Insulin Adjustment

• Increase each meal dose by 1–2 units every 3 days based on 2-hour post-meal glucose 6.
• Target post-prandial glucose: <180 mg/dL 6.

Hypoglycemia Management

• If glucose falls <70 mg/dL, treat immediately with 15 g fast-acting carbohydrate and reduce the implicated insulin dose by 10–20% 6.

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Monitoring Requirements

• Check glucose before each meal and at bedtime (four times daily minimum) 1, 6, 3.
• Daily fasting glucose guides basal insulin titration 6.
• Two-hour post-prandial glucose guides prandial insulin adjustments 6.

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Critical Pitfalls to Avoid

• Never use sliding-scale insulin as the sole regimen in a patient requiring insulin therapy—this approach is inferior, unsafe, and condemned by all major diabetes guidelines 1, 2, 3.
• Do not delay scheduled insulin initiation when glucose is consistently 300–320 mg/dL; this prolongs hyperglycemia exposure and increases complication risk 1, 6.
• Do not give rapid-acting insulin at bedtime as a sole correction dose, as this markedly increases nocturnal hypoglycemia risk 1, 6.
• Do not start metformin in a hospitalized patient with acute infection due to lactic acidosis risk 1.

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Why This Patient Likely Has New-Onset Type 2 Diabetes

• Stress hyperglycemia from cellulitis can unmask previously undiagnosed diabetes 7.
• Glucose levels of 300–320 mg/dL are too high to be explained by stress alone in a patient without underlying diabetes 1, 6.
• This patient will require outpatient follow-up with HbA1c testing after discharge to confirm the diagnosis and guide long-term therapy 6.

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Expected Outcomes with Basal-Bolus Therapy

• 68% of patients achieve mean glucose <140 mg/dL with basal-bolus therapy versus 38% with sliding-scale alone 1, 4.
• No increase in hypoglycemia incidence when basal-bolus regimens are correctly implemented compared with sliding-scale monotherapy 1, 4.
• Target glucose range for non-critically ill hospitalized patients: 140–180 mg/dL 5, 3.