What is the usage and dosage of Humulin N (NPH insulin) in diabetes mellitus management?

Humulin N (NPH Insulin) Usage and Dosage in Diabetes Management

Overview

Humulin N (NPH insulin) is an intermediate-acting insulin with a peak action at 4-6 hours and duration of approximately 12-19 hours, making it particularly useful for basal insulin coverage in twice-daily regimens, enteral/parenteral nutrition, and steroid-induced hyperglycemia. 1

Primary Clinical Applications

Basal Insulin Coverage in Standard Regimens

• NPH insulin is typically administered twice daily (every 12 hours) or three times daily (every 8 hours) as part of a basal-bolus insulin regimen 1
• When combined with rapid-acting or regular insulin before meals, NPH provides intermediate-acting basal coverage that bridges between prandial doses 2
• The standard approach involves NPH administration before breakfast and at bedtime, or before breakfast and dinner 2, 3

Enteral and Parenteral Nutrition

For patients receiving continuous enteral tube feedings, NPH insulin should be administered every 8-12 hours to cover nutritional needs 1

Dosing for Enteral Nutrition:

• Starting dose for insulin-naive patients: 5 units NPH subcutaneously every 12 hours 1
• Nutritional component calculation: 1 unit of insulin per 10-15 grams of carbohydrate in the enteral formula 1
• Adjustments must be made frequently based on point-of-care glucose monitoring 1
• Critical safety measure: If enteral nutrition is interrupted, immediately start 10% dextrose infusion to prevent hypoglycemia 1

Correctional Insulin:

• Administer subcutaneously every 6 hours using regular human insulin 1
• Alternatively, use rapid-acting insulin every 4 hours 1

Bolus Enteral Feedings:

• Give 1 unit of regular or rapid-acting insulin per 10-15 grams of carbohydrate before each feeding 1
• Add correctional insulin as needed before each feeding 1

Steroid-Induced Hyperglycemia

NPH insulin is the specifically recommended insulin formulation for steroid-induced hyperglycemia because its 4-6 hour peak action aligns perfectly with the peak hyperglycemic effect of morning prednisone or other intermediate-acting glucocorticoids 1, 4, 5

Initial Dosing:

• Start with 0.1-0.2 units/kg/day of NPH insulin, administered in the morning concomitantly with steroid administration 4, 6, 5
• NPH is given in addition to the patient's existing basal insulin or oral diabetes medications 1, 4

High-Dose Glucocorticoid Management:

• For high-dose glucocorticoids, insulin requirements typically increase by 40-60% above standard dosing 1, 4, 6
• Increasing doses of prandial and correctional insulin are often needed in addition to basal and NPH insulin 1

Adjustment Protocol:

• Monitor blood glucose every 2-4 hours initially, with special attention to afternoon and evening values when steroid effect peaks 4, 6, 5
• Target blood glucose range: 80-180 mg/dL 1, 4
• Increase NPH dose by 2 units every 3 days until target glucose is achieved 6, 5

Long-Acting Glucocorticoids (Dexamethasone):

• For dexamethasone or continuous glucocorticoid use, a combination of long-acting basal insulin AND NPH insulin may be required 1, 6
• The long-acting insulin manages fasting glucose while NPH covers daytime hyperglycemia 1, 6

Pharmacokinetic Profile

• Peak action: 4-6 hours after subcutaneous injection 1, 7
• Duration of action: Approximately 12-19 hours 7
• Maximal glucose-lowering effect occurs 5-7 hours post-injection 7
• Returns to baseline insulin action within 16-19 hours 7

Critical Safety Considerations

Hypoglycemia Prevention:

• When steroids are discontinued or tapered, insulin requirements decrease rapidly—promptly reduce NPH doses to avoid hypoglycemia 1, 4, 6, 5
• Patients on morning steroid regimens often reach normal glucose levels overnight, creating risk for nocturnal hypoglycemia if long-acting insulin is used instead of NPH 1, 5
• If enteral nutrition is interrupted, immediately start dextrose infusion 1

Common Pitfalls to Avoid:

• Do not rely solely on long-acting insulin for steroid-induced hyperglycemia—this leads to inadequate daytime coverage and potential nocturnal hypoglycemia 4, 5
• Do not use sliding scale insulin alone—it is associated with poor glycemic control 6
• Avoid single daily NPH dosing for continuous enteral nutrition—use twice or three times daily administration 1

Monitoring Requirements

• Point-of-care glucose monitoring before meals and at bedtime 6, 5
• For hospitalized patients on enteral nutrition: monitor every 6 hours initially 1
• For steroid-induced hyperglycemia: monitor every 2-4 hours initially, then before meals and bedtime once stable 4, 6, 5
• Daily adjustments based on glucose patterns and anticipated changes in clinical status are critical 1

Combination Therapy

• NPH can be safely mixed with regular human insulin from different manufacturers without loss of efficacy 8
• When combined with rapid-acting insulin analogs (lispro, aspart), NPH provides effective basal coverage while the rapid-acting insulin manages prandial glucose 9, 2
• For twice-daily regimens: NPH plus rapid-acting insulin before breakfast and dinner improves postprandial control without increasing hypoglycemia risk 2