A patient on insulin Mixtard (biphasic human insulin 70/30) has a pre‑dinner blood glucose of 193 mg/dL; how many units of Mixtard should be administered?

Pre-Dinner Insulin Dosing for Mixtard 70/30

For a pre-dinner blood glucose of 193 mg/dL on Mixtard 70/30, administer the patient's usual scheduled evening dose plus add 2 units as a correction dose, since 193 mg/dL falls above 180 mg/dL but below 250 mg/dL.

Understanding Mixtard 70/30 Dosing Structure

• Mixtard 70/30 contains 70% NPH (intermediate-acting) and 30% regular insulin, administered twice daily before breakfast and before dinner 1.
• The evening dose provides both overnight basal coverage (from the NPH component) and dinner prandial coverage (from the regular insulin component) 1.
• The typical morning-to-evening dose distribution is approximately 60:40 to 67:33 (2/3 morning, 1/3 evening), though this varies by individual insulin resistance patterns 2, 3.

Correction Insulin Protocol for Pre-Dinner Glucose of 193 mg/dL

• Add 2 units of correction insulin to the scheduled evening Mixtard dose when pre-meal glucose is 180–250 mg/dL 4.
• This correction dose supplements—not replaces—the scheduled insulin and addresses the current hyperglycemia while the regular insulin component covers the dinner meal 4.
• The NPH component will provide overnight basal coverage regardless of the correction dose 2.

Systematic Titration of the Evening Mixtard Dose

• If pre-dinner glucose remains ≥180 mg/dL on multiple occasions, increase the scheduled evening Mixtard dose by 2 units every 3 days until pre-dinner values consistently fall within 80–130 mg/dL 4.
• The evening dose adjustment is guided by fasting glucose readings (which reflect overnight NPH action) and pre-dinner glucose (which reflects morning dose adequacy) 2.
• Target pre-dinner glucose is 80–130 mg/dL for optimal glycemic control 4.

When the Scheduled Dose Is Unknown

• If the patient's usual evening Mixtard dose is not documented, calculate an initial total daily dose of 0.3–0.5 units/kg/day for patients with moderate hyperglycemia 4.
• Allocate approximately 33–40% of the total daily dose to the evening injection (before dinner) 2, 3.
• For a 70 kg patient, this translates to approximately 7–14 units as the evening dose, with the remainder given before breakfast 4, 2.

Critical Monitoring Points

• Check fasting glucose daily to assess overnight NPH adequacy and guide evening dose titration 4.
• Measure pre-dinner glucose to evaluate morning dose effectiveness and determine if correction insulin is needed 4.
• Obtain a bedtime glucose (2–3 hours post-dinner) to confirm the regular insulin component is adequately covering the dinner meal 4.

Advancing Beyond Twice-Daily Premixed Insulin

• When the total daily Mixtard dose exceeds 0.5 units/kg/day without achieving HbA1c targets, consider transitioning to a basal-bolus regimen (long-acting basal insulin plus rapid-acting insulin before each meal) rather than further escalating premixed insulin 2.
• Signs that premixed insulin is insufficient include persistent pre-dinner hyperglycemia despite adequate fasting glucose, marked glucose variability, or recurrent hypoglycemia alternating with hyperglycemia 2.

Common Pitfalls to Avoid

• Do not withhold the scheduled evening Mixtard dose and rely solely on correction insulin; the NPH component is essential for overnight basal coverage 4, 2.
• Do not delay systematic titration of the evening dose when pre-dinner glucose repeatedly exceeds 180 mg/dL; adjust every 3 days based on glucose patterns 4, 2.
• Avoid administering correction insulin at bedtime as a sole dose without the scheduled Mixtard, as this markedly raises nocturnal hypoglycemia risk 4.
• Do not continue escalating Mixtard beyond 0.5 units/kg/day without addressing post-prandial hyperglycemia with a more flexible regimen 2.

Hypoglycemia Management

• Treat any glucose <70 mg/dL immediately with 15 g of fast-acting carbohydrate, recheck in 15 minutes, and repeat if needed 4.
• If unexplained hypoglycemia occurs, reduce the implicated dose (morning or evening) by 10–20% before the next administration 4, 2.

Alternative Premixed Formulations

• Mixtard 50/50 (50% regular, 50% NPH) provides more rapid-acting insulin and may be more appropriate for patients with significant post-breakfast or post-dinner hyperglycemia, as it delivers greater prandial coverage 5, 6.
• The choice between Mixtard 30/70 and 50/50 depends on the patient's specific glucose patterns, with 50/50 offering better post-prandial control at the expense of slightly higher hypoglycemia risk 5, 6.