What is the required additional dose of insulin per day for a patient with a history of diabetes and asthma, currently admitted with an asthma exacerbation, who is started on methylprednisolone (steroid) 40mg once daily, and is already on Human Mixtard (insulin) 34-0-16 with an HbA1c (glycated hemoglobin) of 14?

Additional Insulin Dosing for Steroid-Induced Hyperglycemia

For this patient on methylprednisolone 40mg daily with poorly controlled diabetes (HbA1c 14%), add approximately 20-30 units of NPH insulin in the morning to the existing Mixtard regimen, representing an additional 0.3-0.4 units/kg/day to counteract steroid-induced hyperglycemia. 1, 2

Understanding Steroid-Induced Hyperglycemia Pattern

• Methylprednisolone causes hyperglycemia that peaks 7-9 hours after administration and persists for at least 24 hours, with predominant afternoon and evening elevations 3, 1
• The hyperglycemic effect is dose-dependent, and 40mg methylprednisolone represents a moderate-to-high dose requiring significant insulin supplementation 1, 4
• The patient's baseline poor control (HbA1c 14%) indicates pre-existing insulin resistance, necessitating higher supplemental doses than typically recommended 4

Specific Insulin Dose Calculation

• Initial supplemental insulin should be 0.1-0.3 units/kg/day for steroid-induced hyperglycemia, but given the HbA1c of 14%, use the higher end at 0.3-0.4 units/kg/day 1, 2
• Assuming a typical body weight of 60-70kg, this translates to 20-28 units of additional insulin daily 2
• For high-dose glucocorticoids in patients with pre-existing poor control, insulin requirements typically increase by 40-60% above standard dosing 1, 2

Optimal Insulin Formulation Choice

• NPH insulin administered in the morning is the preferred formulation for steroid-induced hyperglycemia because its intermediate-acting profile (peaks at 4-6 hours) aligns with the peak hyperglycemic effect of morning methylprednisolone 1, 2
• Long-acting basal insulins like glargine may under-treat daytime hyperglycemia and cause nocturnal hypoglycemia when used for steroid coverage 4
• The existing Mixtard regimen (34-0-16 units) should be maintained, with NPH added specifically for steroid coverage 2

Practical Implementation Algorithm

Day 1-3:

• Add 24 units NPH insulin in the morning (administered with or just after the methylprednisolone dose) 1, 2
• Monitor blood glucose every 4-6 hours, particularly focusing on afternoon and evening values when steroid effect peaks 3, 1
• Target blood glucose range of 100-180 mg/dL during steroid therapy 1

Day 4 onwards:

• If afternoon/evening glucose remains >180 mg/dL, increase NPH by 2 units every 3 days until target achieved 1, 2
• If hypoglycemia occurs (glucose <70 mg/dL), reduce NPH dose by 10-20% immediately 2
• Consider splitting NPH to twice daily (2/3 morning, 1/3 evening) if midday-to-midnight hyperglycemia persists despite dose adjustments 2

Critical Monitoring Requirements

• Check blood glucose every 4-6 hours for the first 24-48 hours after starting supplemental insulin to identify patterns and guide adjustments 1, 2
• Pay particular attention to overnight and fasting values, as the existing Mixtard evening dose may cause nocturnal hypoglycemia when combined with NPH 1
• The combination of pre-existing poor control and steroid therapy creates high risk for both severe hyperglycemia and treatment-induced hypoglycemia 5, 4

Adjustments During Steroid Taper

• When methylprednisolone is tapered or discontinued, reduce NPH dose by 20% for each 50% reduction in steroid dose to prevent hypoglycemia 3, 2
• Insulin requirements can decline rapidly once steroid effect wanes, typically within 24-48 hours of discontinuation 3
• The transition period is high-risk for hypoglycemia if insulin doses are not appropriately reduced 3

Common Pitfalls to Avoid

• The most dangerous error is failing to add sufficient insulin initially, leading to prolonged severe hyperglycemia that increases hospitalization time and worsens asthma outcomes 5
• Hyperglycemia is a significant factor increasing the risk of extending hospitalization time due to asthma exacerbation, regardless of insulin therapy method 5
• Do not use inhaled insulin in this patient, as it is contraindicated in patients with asthma and chronic lung disease 6, 7
• Avoid maintaining increased insulin doses beyond 24-48 hours after steroid discontinuation, as this creates severe hypoglycemia risk 3

Alternative Approach for Severe Cases

• If target glucose range is not achieved with NPH supplementation, consider an initial daily insulin dose of 0.5 units/kg bodyweight (approximately 30-35 units NPH) or a greater than 30% increase in total pre-steroid insulin dose 4
• For patients with very poor baseline control (HbA1c >12%), larger insulin dose adjustments are typically required 4
• If glycemic control remains suboptimal with once-daily morning NPH, split the dose to twice daily administration 2