Patient on split neutral protamine Hagedorn (NPH) insulin 16 units twice daily and metformin 500 mg daily has hyperglycemia; should a long‑acting basal insulin be added?

Optimize the Current Regimen Before Adding Long-Acting Insulin

The patient does not need a long-acting basal insulin added; instead, the existing NPH 70/30 regimen should be optimized by increasing the dose and maximizing metformin, as NPH 70/30 already contains intermediate-acting insulin that provides basal coverage. 1

Understanding NPH 70/30 Composition

• NPH 70/30 is a premixed insulin containing 70% intermediate-acting NPH insulin (which provides basal coverage) and 30% rapid-acting insulin (which covers meals). 2
• The current dose of 16 units twice daily provides only approximately 11 units of NPH per day (70% of 16 units), which is insufficient for most adults with type 2 diabetes. 1
• Adding a separate long-acting insulin would create redundant basal coverage and increase the risk of hypoglycemia without addressing the fundamental problem of inadequate total insulin dosing. 1

Step-by-Step Optimization Algorithm

Step 1: Increase NPH 70/30 Dose Immediately

• Increase NPH 70/30 to 24-28 units twice daily (before breakfast and dinner), which represents a 50-75% increase from the current dose. 1
• For a patient with blood glucose of 324 mg/dL, insulin requirements are typically 0.3-0.5 units/kg/day; assuming a 70-80 kg patient, total daily insulin should be 21-40 units, far exceeding the current 32 units total. 1, 3
• The dose should be titrated upward by 2-4 units every 3 days until fasting glucose reaches 100-180 mg/dL and post-meal glucose remains below 180 mg/dL. 1, 3

Step 2: Maximize Metformin Dose

• Increase metformin from 500 mg daily to 1000 mg twice daily (total 2000 mg/day), provided renal function is adequate (eGFR >30 mL/min). 1, 4
• Metformin enhances peripheral insulin sensitivity, reduces hepatic glucose production, and when combined with insulin provides superior glycemic control compared to insulin monotherapy. 4, 5, 6
• The combination of metformin with insulin also reduces weight gain compared to insulin alone, an important quality-of-life consideration. 6, 7

Step 3: Implement Structured Glucose Monitoring

• Check capillary glucose four times daily: fasting, 2 hours after breakfast, 2 hours after dinner, and at bedtime. 1
• Target glucose range is 100-180 mg/dL throughout the day. 1, 3
• The fasting glucose reflects overnight NPH coverage from the evening dose, while post-meal readings assess the rapid-acting component. 1

Why Long-Acting Insulin Is Not Indicated

Redundancy of Basal Coverage

• NPH 70/30 already contains intermediate-acting insulin that provides 12-16 hours of basal coverage per dose. 2
• Adding glargine, detemir, or degludec would create overlapping basal insulin action, substantially increasing hypoglycemia risk without improving glycemic control. 1, 6

Evidence Supporting NPH-Based Regimens

• Multiple randomized controlled trials demonstrate that twice-daily NPH insulin combined with metformin provides glycemic control comparable to basal-bolus regimens (long-acting insulin plus mealtime insulin). 6, 7
• The LANMET study showed that bedtime NPH plus metformin achieved mean HbA1c of 7.14% with appropriate dose titration, equivalent to insulin glargine plus metformin. 7
• Premixed insulins containing NPH (such as 70/30) are specifically recommended for patients requiring both basal and prandial coverage in a simplified regimen. 8, 2

When to Consider Long-Acting Insulin

Long-acting basal insulin becomes appropriate only if the patient:

• Requires more than 60-80 units of NPH 70/30 twice daily and still has inadequate fasting glucose control, suggesting the need for separate basal and prandial insulin. 1
• Experiences recurrent nocturnal hypoglycemia despite dose adjustments, indicating that the NPH component is peaking excessively overnight. 7
• Is started on high-dose glucocorticoids (e.g., prednisone >40 mg/day), which may require additional long-acting basal insulin to control fasting hyperglycemia. 1

Common Pitfalls to Avoid

• Do not add long-acting insulin prematurely when the existing regimen has not been optimized; this creates unnecessary complexity and cost. 1, 6
• Do not rely on fasting glucose alone to assess control; post-meal glucose elevations are equally important and may indicate inadequate prandial insulin coverage. 1
• Do not increase insulin without maximizing metformin first, as metformin reduces insulin requirements by 43% on average and mitigates weight gain. 6
• Do not use sliding-scale correction insulin alone; scheduled insulin doses based on anticipated needs provide superior glycemic control. 1