How do you adjust insulin doses during chemotherapy?

Insulin Adjustment During Chemotherapy

Increase insulin doses significantly during chemotherapy—particularly when dexamethasone or other corticosteroids are administered—using NPH insulin in the morning to match the afternoon/evening hyperglycemic pattern, and monitor glucose closely with adjustments made more aggressively than usual. 1

Understanding Chemotherapy-Induced Hyperglycemia

Chemotherapy, especially regimens containing dexamethasone or other corticosteroids, causes predictable hyperglycemia that requires proactive insulin adjustment:

• All patients receiving chemotherapy with dexamethasone experience hyperglycemia, regardless of baseline diabetes status 2
• The hyperglycemic effect peaks in the afternoon and evening, corresponding to steroid pharmacokinetics 1
• Patients without baseline diabetes spend 3.9% of time hyperglycemic, those with prediabetes 10%, and those with diabetes 73.3% of time during chemotherapy 2

Specific Insulin Adjustment Strategy

For Steroid-Containing Chemotherapy Regimens

NPH insulin given in the morning is the preferred basal insulin over long-acting analogs like glargine, as it provides better coverage for the peak hyperglycemic periods caused by steroids 1:

• Calculate NPH dose at 0.3-0.4 units/kg bodyweight for patients on high-dose corticosteroids 1
• If not previously on insulin, start with 0.5 units/kg total daily dose, or increase pre-existing insulin by more than 30% 1
• Administer NPH in the morning to match the afternoon/evening hyperglycemic pattern 1

Prandial Insulin Distribution

Emphasize lunch and dinner insulin doses when steroid effects peak 1:

• Distribute prandial insulin with heavier weighting toward later meals (example: 6 units breakfast, 10 units lunch, 10 units dinner for a typical patient) 1
• Use rapid-acting analogs (lispro, aspart, or glulisine) before meals 3
• Calculate using insulin-to-carbohydrate ratio of approximately 1:10 for conservative dosing 1

Correction Doses

Use a simplified sliding scale for supplemental correction 1:

• For premeal glucose >250 mg/dL (>13.9 mmol/L): add 2 units of rapid-acting insulin 1
• For premeal glucose >350 mg/dL (>19.4 mmol/L): add 4 units of rapid-acting insulin 1

Critical Monitoring Requirements

Monitor blood glucose before lunch and dinner when steroid effects are maximal 1:

• Target premeal glucose of 90-150 mg/dL (5.0-8.3 mmol/L) 1
• Check fasting glucose to guide NPH dose adjustments 4
• Consider continuous glucose monitoring during chemotherapy cycles to identify patterns 2

Dose Titration Principles

Increase insulin doses by larger increments than usual during active chemotherapy 1:

• Adjust doses every 2 weeks based on premeal glucose readings 5
• If 50% of premeal values over 2 weeks are above target, increase the dose 5
• Reduce insulin immediately when steroids are stopped to prevent severe hypoglycemia 1

Critical Safety Considerations

Never use rapid- or short-acting insulin at bedtime to avoid nocturnal hypoglycemia 3, 1:

• This is especially important during chemotherapy when eating patterns may be disrupted 5
• Patients should carry at least 15g carbohydrate for hypoglycemia treatment 5
• Continue insulin even if the patient is unable to eat or is vomiting during chemotherapy 5

Special Populations and Considerations

Patients Without Pre-existing Diabetes

• Screen all patients receiving dexamethasone-containing chemotherapy for hyperglycemia 6
• Initiate insulin therapy proactively rather than waiting for severe hyperglycemia 6
• Fasting blood glucose and HbA1c are the most commonly used indicators for treatment decisions 4

Elderly or Frail Patients

• Use relaxed glucose targets (90-150 mg/dL premeal) to minimize hypoglycemia risk 1
• Consider morning NPH timing to reduce nocturnal hypoglycemia risk 1
• Simplify regimens when possible while maintaining adequate control 5

Common Pitfalls to Avoid

Do not use only sliding scale insulin without basal coverage, as this leads to poor glycemic control 3:

• Basal insulin must be continued throughout chemotherapy 5
• Avoid mixing rapid-acting analogs with basal insulin in the same syringe 3
• Do not underestimate the magnitude of insulin increase needed during high-dose steroid therapy 1

Alternative Considerations

While intensive insulin therapy improves glycemic control during chemotherapy, secondary evidence suggests metformin and thiazolidinediones may be associated with improved cancer outcomes compared to high-dose exogenous insulin 7. However, this should not prevent adequate glycemic control with insulin when needed 7.

Self-monitoring of blood glucose is essential for all insulin-using patients during chemotherapy, with dose adjustments based on measured glucose values 5.

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