What is the recommended approach when switching from insulin NPH (Neutral Protamine Hagedorn) to 70/30 (premixed insulin)?

Switching from NPH to 70/30 Premixed Insulin

When switching from NPH insulin to 70/30 premixed insulin, calculate 80% of the current total daily NPH dose, then divide into two injections with 2/3 given before breakfast and 1/3 given before dinner.

Conversion Process

The American Diabetes Association provides clear guidance on transitioning from NPH to premixed insulin 1:

1. Calculate the new total daily dose:

   • Use 80% of the current total daily NPH dose
   • Example: If patient is on 60 units NPH daily → 60 × 0.8 = 48 units total daily dose of 70/30 insulin

2. Split the dose:

   • Morning dose: 2/3 of total (before breakfast)
   • Evening dose: 1/3 of total (before dinner)
   • Example: 48 units total → 32 units before breakfast, 16 units before dinner

3. Timing of administration:

   • For 70/30 NPH/regular: Administer 30 minutes before meals
   • For 70/30 aspart mix or 75/25 lispro mix: Administer 0-15 minutes before meals 2

Monitoring and Adjustment

• Check blood glucose before breakfast, lunch, dinner, and bedtime
• Adjust morning dose based on pre-dinner glucose readings
• Adjust evening dose based on fasting morning glucose readings 2
• Titrate each component of the plan based on individualized needs 1

Rationale for Switching

The ADA guidelines specifically note that adding prandial insulin to NPH may warrant consideration of a premixed insulin plan to decrease the number of injections required 1. This approach provides both basal and prandial coverage in a single injection, addressing both fasting and postprandial glucose excursions.

Special Considerations

1. Hypoglycemia risk:

   • The 80% conversion rule helps reduce the risk of hypoglycemia during transition
   • Monitor closely for hypoglycemia during the first 1-2 weeks after switching

2. Meal consistency:

   • Premixed insulins work best with consistent meal timing and carbohydrate content
   • Irregular meal patterns may increase risk of hypoglycemia or hyperglycemia 2

3. Hospital settings:

   • Note that premixed insulin therapy (70/30) has been associated with high rates of iatrogenic hypoglycemia in hospital settings and is not recommended for inpatient use 1

4. Elderly patients:

   • For older adults, a simplified insulin regimen may be beneficial
   • The ADA provides specific guidance for insulin simplification in older adults 1

Common Pitfalls to Avoid

1. Direct unit-for-unit conversion:

   • Never convert directly from NPH to 70/30 without the 80% adjustment
   • This can lead to hypoglycemia due to the different pharmacokinetic profiles

2. Inconsistent administration timing:

   • Ensure proper timing before meals based on the specific premixed formulation
   • Inconsistent timing can lead to variable glycemic control

3. Ignoring meal patterns:

   • Assess patient's meal timing consistency before switching
   • Patients with highly variable meal schedules may not be ideal candidates

4. Overbasalization:

   • Avoid continuing to escalate doses without meaningful glucose improvements
   • Consider alternative approaches if premixed insulin fails to achieve targets

By following this structured approach to transitioning from NPH to 70/30 premixed insulin, clinicians can help patients achieve improved glycemic control while minimizing the risk of hypoglycemia and reducing the burden of multiple daily injections.