What initial insulin glargine dose, insulin sensitivity factor, and carbohydrate‑to‑insulin ratio should be used for a 23‑year‑old obese male with type 2 diabetes (A1c 13 %), metabolic syndrome, mild metabolic acidosis, low‑grade ketosis, on metformin 2000 mg daily, admitted for cellulitis?

Insulin Dosing for Hospitalized Type 2 Diabetes with Ketosis and Severe Hyperglycemia

Start insulin glargine (Lantus) at 0.5 units/kg/day (approximately 61 units once daily at bedtime for this 122 kg patient), use an insulin sensitivity factor (correction factor) of 1:30 initially (1 unit lowers glucose by 30 mg/dL), and begin with a carbohydrate ratio of 1:10 (1 unit per 10 grams of carbohydrate). 1, 2, 3

Immediate Assessment and Stabilization

This patient presents with mild diabetic ketoacidosis (DKA) based on bicarbonate 17 mEq/L (below the 18 mEq/L threshold), anion gap 16, and ketones 1.28, though the exact glucose level is not provided. 4, 2

Critical First Steps

• Verify renal function before continuing metformin – metformin must be held if eGFR <30 mL/min/1.73 m² and is contraindicated during acute illness with risk of lactic acidosis, particularly with cellulitis and potential sepsis. 2, 5, 6

• Check venous pH immediately – if pH <7.3, this patient requires IV insulin infusion at 0.1 units/kg/hour (approximately 12 units/hour) until resolution of acidosis (pH >7.3, bicarbonate >18 mEq/L, anion gap <12). 4, 3

• Assess hydration status and initiate fluid resuscitation with isotonic saline while monitoring electrolytes every 2-4 hours, particularly potassium. 4, 3

Basal Insulin Dosing (Lantus)

For this 122 kg patient with A1c 13% and mild ketosis, initiate insulin glargine at 0.5 units/kg/day = 61 units once daily at bedtime. 1, 2, 3

Rationale for Higher Dosing

• The American Diabetes Association recommends 0.5 units/kg/day (not the lower 0.1-0.2 units/kg/day) for patients with A1c ≥8.5% and marked hyperglycemia, which clearly applies here with A1c 13%. 2, 3

• Obesity (BMI 41) and severe insulin resistance in metabolic syndrome require higher initial doses to overcome glucose toxicity. 1

• This patient likely has prolonged poor glycemic control given the severely elevated A1c, necessitating aggressive initial therapy. 1, 3

Titration Protocol

• Increase basal insulin by 2-4 units every 3 days based on fasting blood glucose, targeting fasting glucose 80-130 mg/dL. 3

• Continue metformin 2000 mg daily once acidosis resolves and renal function is confirmed adequate (eGFR ≥30 mL/min/1.73 m²). 1, 2

Correction Scale (Insulin Sensitivity Factor)

Use an initial correction factor of 1:30 – meaning 1 unit of rapid-acting insulin (aspart, lispro, or glulisine) will lower blood glucose by approximately 30 mg/dL. 3

Calculation Method

• The "1800 rule" for type 2 diabetes: 1800 ÷ total daily insulin dose = correction factor. 3

• With estimated total daily dose of 61 units basal (will need prandial insulin added), initial correction factor = 1800 ÷ 61 ≈ 1:30. 3

Correction Scale Example

• Blood glucose 151-200 mg/dL: Give 2 units rapid-acting insulin
• Blood glucose 201-250 mg/dL: Give 3 units rapid-acting insulin
• Blood glucose 251-300 mg/dL: Give 5 units rapid-acting insulin
• Blood glucose 301-350 mg/dL: Give 7 units rapid-acting insulin
• Blood glucose >350 mg/dL: Give 9 units and notify physician 3

Critical pitfall: Never use correction insulin alone without basal coverage – sliding scale monotherapy leads to poor outcomes and increased complications. 3

Carbohydrate Ratio

Start with a carbohydrate-to-insulin ratio of 1:10 – meaning 1 unit of rapid-acting insulin covers 10 grams of carbohydrate. 3

Prandial Insulin Requirements

• This patient requires basal-bolus therapy, not basal insulin alone, given the severity of hyperglycemia (A1c 13%). 3

• Calculate prandial insulin as 50% of total daily dose divided among three meals: If total daily dose is 61 units basal, add approximately 61 units prandial = 122 units total daily dose, with roughly 20 units rapid-acting insulin before each meal. 3

• Adjust prandial insulin by 1-2 units every 3 days based on 2-hour postprandial glucose readings, targeting postprandial glucose <180 mg/dL. 3

Carbohydrate Ratio Calculation

• The "500 rule": 500 ÷ total daily insulin dose = grams of carbohydrate covered by 1 unit. 3

• With total daily dose of approximately 122 units: 500 ÷ 122 ≈ 1:4, but start more conservatively at 1:10 to avoid hypoglycemia and titrate based on response. 3

Monitoring Requirements During Hospitalization

• Check blood glucose at least 4 times daily – before each meal and at bedtime, plus additional checks if symptomatic. 3

• Monitor serum electrolytes, glucose, BUN, creatinine, and venous pH every 2-4 hours until acidosis resolves (bicarbonate >18 mEq/L, anion gap <12). 4, 3

• Potassium replacement is critical – add 20-30 mEq potassium (2/3 KCl and 1/3 KPO4) to each liter of IV fluid once serum potassium falls below 5.5 mEq/L, assuming adequate urine output. 4

Transition and Long-Term Management

• Once glucose control is achieved and acidosis resolves, attempt to taper insulin by decreasing the dose 10-30% every few days while maintaining metformin 2000 mg daily. 1, 2

• Recheck A1c in 3 months – if A1c remains ≥7% despite maximum metformin, add a GLP-1 receptor agonist or SGLT2 inhibitor before further intensifying insulin. 1, 2

• Many patients with type 2 diabetes can transition off insulin to oral agents alone once glucotoxicity resolves, though this patient's severe presentation may require long-term insulin therapy. 1

Common Pitfall to Avoid

Do not restart metformin until the cellulitis is resolving and metabolic acidosis has completely cleared – the combination of infection, acidosis, and metformin significantly increases lactic acidosis risk. 2, 5, 6