Can I give short-acting insulin (e.g. aspart, glulisine, or lispro) to a patient with severe hyperglycemia and on metformin (1g controlled release) and if so, what dose?

Management of Severe Hyperglycemia with Short-Acting Insulin

Yes, you should give short-acting insulin immediately for a blood glucose level of 23 mmol/L (414 mg/dL), and the recommended starting dose is 4-6 units of rapid-acting insulin (aspart, lispro, or glulisine) subcutaneously, with repeat dosing every 4-6 hours based on blood glucose monitoring. 1

Immediate Insulin Therapy Rationale

• Severe hyperglycemia at this level (>16.7 mmol/L or >300 mg/dL) requires immediate insulin therapy regardless of current oral medications. 1
• The patient's blood glucose of 23 mmol/L represents a medical urgency that metformin alone cannot adequately address, even at the current dose of 1g controlled release. 1
• Continue metformin unless contraindicated (check renal function), as it remains the foundation of therapy and should not be stopped when adding insulin. 1

Specific Dosing Algorithm for Short-Acting Insulin

Initial Correction Dose

• Start with 4-6 units of rapid-acting insulin (aspart, lispro, or glulisine) subcutaneously for this level of hyperglycemia. 1, 2
• These rapid-acting analogs provide better postprandial glucose control than regular human insulin due to their faster onset and shorter duration of action. 1, 3, 4

Monitoring and Repeat Dosing

• Check blood glucose every 2-4 hours and administer additional correction doses of short-acting insulin as needed. 1
• For blood glucose >180 mg/dL (10 mmol/L), give correction doses before meals or every 6 hours if the patient is not eating. 1

Transition to Structured Insulin Regimen

This patient will likely require a basal-bolus insulin regimen, not just correction insulin alone. 1, 2

Basal Insulin Addition

• Initiate basal insulin (glargine, detemir, or degludec) at 0.2-0.3 units/kg/day given the severity of hyperglycemia. 1, 2
• For severe hyperglycemia (>300 mg/dL), a total daily insulin dose of 0.3-0.5 units/kg is appropriate, with half given as basal and half as prandial insulin. 1, 2

Prandial Insulin Coverage

• Add 4 units of rapid-acting insulin before each meal (or 10% of the basal dose) once the patient is eating regularly. 2
• Rapid-acting insulin analogs (aspart, lispro, glulisine) should be dosed just before meals for optimal postprandial control. 1, 3

Critical Pitfalls to Avoid

• Do not rely solely on sliding-scale correction insulin without a structured basal-bolus regimen, as this approach is suboptimal and associated with poor glycemic control. 1, 2
• Do not delay insulin therapy in patients with severe hyperglycemia—immediate treatment is mandatory to prevent metabolic decompensation. 1
• Do not stop metformin unless there are contraindications (renal dysfunction, contrast studies, or acute illness affecting renal function). 1, 5
• Monitor for hypoglycemia once insulin is initiated, particularly overnight, and adjust doses accordingly. 1

Assessment for Diabetic Ketoacidosis

• Check for ketones (urine or blood) and assess for symptoms of diabetic ketoacidosis (DKA) given the severe hyperglycemia. 1
• If ketones are present or the patient has catabolic features (weight loss, dehydration), continuous intravenous insulin infusion may be required instead of subcutaneous insulin. 1

Patient Education Requirements

• Teach proper insulin injection technique, recognition and treatment of hypoglycemia, self-monitoring of blood glucose, and "sick day" management rules. 1, 2
• Explain that insulin therapy may be temporary if this represents acute decompensation, with potential transition back to oral agents once glucose is controlled. 1