What is the NPH (Neutral Protamine Hagedorn) insulin dose correction scale and carb coverage for a patient with cystic fibrosis starting on prednisone (corticosteroid) 30 mg?

Steroid-Induced Hyperglycemia Management in Cystic Fibrosis

Direct Answer

For a 52-year-old, 64 kg female with cystic fibrosis starting prednisone 30 mg daily, initiate NPH insulin at 0.3-0.5 units/kg/day (approximately 19-32 units total daily dose), given as a single morning dose before breakfast, with correction scale insulin (rapid-acting) before meals starting at 1 unit per 50 mg/dL above 150 mg/dL, and carbohydrate coverage at 1 unit per 15 grams of carbohydrates. 1, 2

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Initial Insulin Dosing Strategy

Total Daily Insulin Requirement

• Start with 0.3-0.5 units/kg/day for steroid-induced hyperglycemia 1, 2
• For this 64 kg patient: 19-32 units total daily dose 2
• If already on insulin, increase pre-existing dose by >30% or 130% of current regimen 2
• Higher starting doses (0.5 units/kg) are warranted given the 30 mg prednisone dose, which is considered high-dose therapy 1

NPH-Specific Dosing

• Give entire NPH dose as a single morning injection before breakfast 1
• NPH is preferred over glargine for steroid-induced hyperglycemia because prednisone causes hyperglycemia predominantly between midday and midnight 2
• Starting NPH dose: approximately 25-30 units before breakfast (using 0.4 units/kg as middle ground) 2

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Correction Scale (Sliding Scale)

Rapid-Acting Insulin Correction Doses

Before each meal and bedtime, use the following correction scale with rapid-acting insulin (aspart, lispro, or glulisine):

• Blood glucose 150-200 mg/dL: 2 units 1
• Blood glucose 201-250 mg/dL: 4 units 1
• Blood glucose 251-300 mg/dL: 6 units 1
• Blood glucose 301-350 mg/dL: 8 units 1
• Blood glucose >350 mg/dL: 10 units and contact provider 1

Target range: 5-10 mmol/L (90-180 mg/dL) 1

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Carbohydrate Coverage

Insulin-to-Carb Ratio

• Start with 1 unit of rapid-acting insulin per 15 grams of carbohydrates 1
• This is a conservative starting ratio appropriate for insulin-naive patients 1
• Adjust based on postprandial glucose readings after 2-3 days 1

Meal Timing

• Administer rapid-acting insulin immediately before each meal 1
• Patient requires 4 injections daily: NPH before breakfast, plus rapid-acting before breakfast, lunch, and dinner 1

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Monitoring Requirements

Blood Glucose Monitoring Frequency

• Check blood glucose 4 times daily minimum: fasting and 2 hours post-meals 1
• Increase to before each meal and bedtime if readings are out of target range 1
• Continue intensive monitoring while on corticosteroids and when significant changes occur 1

Warning Signs

• Blood glucose persistently ≥270 mg/dL (15 mmol/L) requires urgent medical review 1
• Blood glucose >360 mg/dL (20 mmol/L) or meter reading "HI": present to hospital immediately for assessment of hyperosmolar hyperglycemic state 1

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Dose Adjustments

Titration Strategy

• Increase insulin doses by 10-20% every 2-3 days if blood glucose remains above target 1, 2
• Larger dose adjustments are often needed in steroid-induced hyperglycemia compared to other diabetes types 2
• As prednisone is tapered, insulin doses must be down-titrated proportionally to prevent hypoglycemia 1

Special Considerations for CF

• Patients with CF have increased prednisolone clearance (60% higher) and may require more frequent or higher steroid doses, potentially worsening hyperglycemia 3
• CF patients typically require lower insulin doses than type 1 diabetes despite intensive regimens 4
• Weight gain is a primary goal in CF; insulin therapy promotes anabolic state and macronutrient retention 1, 4

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Critical Pitfalls to Avoid

Common Errors

• Do not rely solely on sliding-scale insulin without basal coverage - this is inadequate for steroid-induced hyperglycemia 5
• Do not use glargine as first-line basal insulin - NPH better matches the midday-to-midnight hyperglycemia pattern of prednisone 2
• Do not use A1C for diagnosis or monitoring in CF - it is not recommended for screening or management 1
• Do not continue high insulin doses as steroids taper - failure to reduce insulin proportionally causes hypoglycemia 1

Monitoring Failures

• Do not ignore persistent hyperglycemia ≥270 mg/dL - this requires immediate medication adjustment 1
• Do not delay endocrinology consultation if glucose control is not achieved within 3-5 days 1

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Long-Term Steroid Considerations

Duration and Adverse Effects

• Chronic corticosteroid use is NOT recommended in CF without specific indications like ABPA or asthma 6, 7, 8
• Prednisone 30 mg daily is considered high-dose therapy (≥30 mg/day) with significant metabolic risks 1
• Glucose abnormalities occur early (within 6 months) with chronic steroid use in CF 7, 8
• Growth retardation, cataracts, and osteoporosis are major concerns with prolonged therapy 9, 7, 8

Alternative Approaches

• If steroids are for CF lung disease exacerbation, limit duration to <24 months if possible 7
• Consider lowest effective dose and shortest duration for any indication 6
• Monitor for development of cystic fibrosis-related diabetes (CFRD) which occurs in 20% of adolescents and 40-50% of adults with CF 1