How do I convert a type 2 diabetic adult patient from Mixtard (biphasic insulin) to a basal-bolus insulin regimen?

Converting Mixtard to Basal-Bolus Insulin in Type 2 Diabetes

Calculate Total Daily Dose from Current Mixtard Regimen

Add up all units of Mixtard currently administered per day to determine the total daily dose (TDD). 1 This becomes the foundation for your basal-bolus conversion.

Apply the 50:50 Split

Divide the TDD using a 50:50 split: give 50% as basal insulin (glargine or detemir) once daily and 50% as prandial insulin (rapid-acting analog like lispro or aspart) divided equally among three meals. 2, 1 For example, if a patient takes 60 units of Mixtard daily, prescribe 30 units of basal insulin once daily and 10 units of rapid-acting insulin before each meal.

Specific Dosing Algorithm

• Basal insulin component: Administer 50% of TDD as insulin glargine (Lantus) once daily at the same time each day, typically in the evening 1
• Prandial insulin component: Divide the remaining 50% equally among three meals as rapid-acting insulin analog (lispro, aspart, or glulisine) given 0-15 minutes before meals 2, 3
• Continue metformin unless contraindicated, as this combination reduces total insulin requirements and provides superior glycemic control with less weight gain 1

Titration Protocol After Conversion

Adjust basal insulin by 2-4 units every 3 days based on fasting glucose until reaching 80-130 mg/dL. 1, 4 If fasting glucose is ≥180 mg/dL, increase by 4 units every 3 days; if 140-179 mg/dL, increase by 2 units every 3 days. 1

Adjust prandial insulin by 1-2 units every 3 days based on 2-hour postprandial glucose readings, targeting <180 mg/dL. 1 Increase the specific meal dose if postprandial glucose consistently exceeds 180 mg/dL after that meal.

Monitoring Requirements

• Check fasting blood glucose daily during titration to guide basal insulin adjustments 1
• Check pre-meal and 2-hour postprandial glucose to guide prandial insulin adjustments 1
• Reassess every 3 days during active titration and every 3-6 months once stable 1

Critical Threshold Warning

When basal insulin exceeds 0.5 units/kg/day without achieving glycemic targets, intensify prandial insulin rather than continuing to escalate basal insulin alone. 1, 5 Signs of "overbasalization" include bedtime-to-morning glucose differential ≥50 mg/dL, hypoglycemia episodes, and high glucose variability. 1, 5

Special Considerations for High-Risk Patients

Reduce the calculated TDD by 20-50% in elderly patients (>65 years), those with renal impairment, or poor oral intake. 1 Use starting doses of 0.1-0.25 units/kg/day for these populations to prevent hypoglycemia. 1

Common Pitfalls to Avoid

• Never use sliding scale insulin as monotherapy after conversion—this leads to dangerous glucose fluctuations and is explicitly condemned by all major guidelines 2, 1
• Never give rapid-acting insulin at bedtime as this significantly increases nocturnal hypoglycemia risk 1
• Never discontinue metformin when converting to basal-bolus insulin unless contraindicated, as this leads to higher insulin requirements and more weight gain 1
• Never continue premixed insulin (Mixtard) in hospitalized patients as randomized trials show significantly increased hypoglycemia rates compared to basal-bolus regimens 1

Patient Education Essentials

Provide education on: proper insulin injection technique and site rotation, recognition and treatment of hypoglycemia (15 grams of fast-acting carbohydrate for glucose ≤70 mg/dL), self-monitoring of blood glucose, "sick day" management rules, and insulin storage and handling. 1