How do I calculate the total daily dose and split the morning and evening units for a premixed 70/30 insulin (70% neutral protamine Hagedorn, 30% regular insulin) in a 70‑kg insulin‑naïve adult with type 2 diabetes?

Calculating 70/30 Insulin Dosing for a 70‑kg Insulin‑Naïve Adult with Type 2 Diabetes

Premixed 70/30 Insulin Is Not Recommended as Initial Therapy

Premixed 70/30 insulin (70% NPH, 30% regular) should not be used for initial insulin therapy in type 2 diabetes because major diabetes guidelines do not recommend it for this purpose, and randomized trials in hospitalized patients showed a 64% hypoglycemia rate versus 24% with basal‑bolus therapy, leading to early trial termination. 11

The fixed 70:30 ratio cannot be adjusted independently, increasing hypoglycemia risk when meal intake varies, and the formulation requires twice‑daily injections (before breakfast and dinner) with consistent meal timing and carbohydrate intake, limiting flexibility for patients with variable eating patterns. 11

Recommended Initial Insulin Regimen: Basal Insulin Alone

For a 70‑kg insulin‑naïve adult with type 2 diabetes, start with basal insulin (glargine or detemir) at 10 units once daily OR 0.1–0.2 units/kg body weight (7–14 units), administered at the same time each day, while continuing metformin unless contraindicated. 221

Titration Protocol for Basal Insulin

• Increase the dose by 2 units every 3 days if fasting glucose is 140–179 mg/dL. 221
• Increase the dose by 4 units every 3 days if fasting glucose is ≥180 mg/dL. 221
• Target fasting glucose: 80–130 mg/dL. 221
• If hypoglycemia (<70 mg/dL) occurs without clear cause, reduce the dose by 10–20% immediately. 221

Critical Threshold: When to Add Prandial Insulin

When basal insulin exceeds 0.5 units/kg/day (35 units for a 70‑kg patient) and approaches 1.0 units/kg/day without achieving HbA1c goals, add prandial insulin (4 units before the largest meal or 10% of basal dose) rather than further basal escalation. 221

This threshold prevents "over‑basalization," which causes hypoglycemia without improving control. 21

If 70/30 Insulin Must Be Used (Against Guideline Recommendations)

Initial Dosing Calculation

For a 70‑kg patient requiring premixed insulin despite guideline recommendations:

• Total daily dose: 0.1–0.2 units/kg/day = 7–14 units/day total. 3
• Morning dose (before breakfast): 2/3 of total = approximately 5–9 units. 4
• Evening dose (before dinner): 1/3 of total = approximately 2–5 units. 4

Administration Timing

• Morning dose: Administer 30 minutes before breakfast (regular insulin component requires this lead time). 53
• Evening dose: Administer 30 minutes before dinner. 53

Titration Protocol for 70/30 Insulin

• Increase the morning dose by 2 units every 3 days if fasting glucose remains 140–179 mg/dL. 22
• Increase the evening dose by 2 units every 3 days if pre‑dinner glucose remains elevated. 22
• Target fasting glucose: 80–130 mg/dL; target pre‑dinner glucose: <180 mg/dL. 22

Monitoring Requirements

• Check fasting glucose daily during titration. 221
• Check pre‑dinner glucose to guide evening dose adjustments. 22
• Measure glucose before each meal and at bedtime (minimum four times daily). 21

Why Basal Insulin Alone Is Superior to 70/30 for Initial Therapy

• Flexibility: Basal insulin can be titrated independently without affecting prandial coverage. 21
• Safety: Randomized trials show premixed insulin carries excessive hypoglycemia risk (64% vs. 24% with basal‑bolus). 1
• Simplicity: Once‑daily basal insulin is easier to manage than twice‑daily premixed injections. 21
• Guideline support: The American Diabetes Association explicitly recommends basal insulin as initial therapy, not premixed formulations. 221

Common Pitfalls to Avoid

• Do not use premixed 70/30 insulin as initial therapy when basal insulin alone is guideline‑recommended and safer. 1
• Do not give equal morning and evening doses of 70/30 insulin—the 2/3:1/3 ratio accounts for greater overnight insulin sensitivity and reduces nocturnal hypoglycemia risk. 4
• Do not discontinue metformin when starting insulin unless contraindicated, as the combination reduces total insulin requirements by 20–30% and provides superior glycemic control. 21
• Do not delay insulin initiation in patients not achieving glycemic goals with oral medications, as this prolongs hyperglycemia exposure and increases complication risk. 21

Expected Clinical Outcomes

• With properly implemented basal insulin therapy, approximately 68% of patients achieve mean glucose <140 mg/dL, compared with only 38% using sliding‑scale insulin alone. 21
• HbA1c reduction of 1.1–1.3% is achievable with once‑daily premixed insulin plus metformin, though basal insulin alone offers comparable efficacy with better safety. 3