What is the recommended approach for switching a patient from Humulin 70/30 (insulin isophane and insulin regular) to Lantus (insulin glargine)?

Switching from Humulin 70/30 to Lantus (Insulin Glargine)

When switching from Humulin 70/30 to Lantus, calculate 80% of the total daily dose of the premixed insulin and administer this as once-daily Lantus, then add rapid-acting insulin (lispro or aspart) before meals to cover prandial needs, starting with 4 units or 10% of the basal dose at the largest meal. 1, 2

Understanding the Conversion Rationale

Humulin 70/30 is a premixed insulin containing 70% intermediate-acting (NPH) and 30% short-acting insulin, providing both basal and prandial coverage in a single injection. 3 Lantus (insulin glargine) is a long-acting basal insulin that provides relatively constant insulin levels over 24 hours with no pronounced peak, fundamentally different from the biphasic action of 70/30. 4, 5

Step-by-Step Conversion Protocol

Calculate Total Daily Dose

• Add up all units of Humulin 70/30 currently administered per day (morning dose + evening dose). 1

Determine Lantus Starting Dose

• When switching from twice-daily NPH-containing insulin (like 70/30) to once-daily Lantus, use 80% of the total daily dose. 2
• For example: If taking 30 units morning + 20 units evening = 50 units total, start Lantus at 40 units once daily. 2
• This dose reduction is critical because the FDA label specifically recommends this approach to lower hypoglycemia risk when transitioning from NPH-based regimens. 2

Add Prandial Insulin Coverage

• Since Lantus only provides basal coverage, you must add rapid-acting insulin (lispro or aspart) before meals to replace the short-acting component of the 70/30. 1
• Start with 4 units of rapid-acting insulin before the largest meal, or use 10% of the basal insulin dose. 1
• If additional prandial coverage is needed, add doses before other meals, titrating based on postprandial glucose readings. 1

Timing Considerations

• Administer Lantus once daily at the same time each day (can be any time, but consistency is essential). 2
• Give rapid-acting insulin 0-15 minutes before meals. 6

Monitoring During Transition

Increase blood glucose monitoring frequency significantly during the first 1-2 weeks after conversion. 2, 7

• Check fasting glucose to assess basal insulin adequacy. 1
• Monitor 2-hour postprandial glucose to evaluate prandial insulin doses. 7
• Watch for hypoglycemia, particularly nocturnal episodes, as Lantus has lower nocturnal hypoglycemia risk than NPH-based insulins. 8

Dose Adjustment Guidelines

• If hypoglycemia occurs without clear cause, reduce the corresponding insulin dose by 10-20%. 1
• Titrate Lantus by increasing 2 units every 3 days to reach fasting plasma glucose goal. 1
• Adjust prandial insulin by 1-2 units or 10-15% based on postprandial glucose patterns. 1

Critical Pitfalls to Avoid

• Never convert unit-for-unit from 70/30 to Lantus alone—this will cause severe hyperglycemia because you're losing the prandial component. 1, 2
• Do not use 100% of the 70/30 dose when converting to Lantus—the 80% reduction is essential to prevent hypoglycemia. 2
• Never mix Lantus with other insulins in the same syringe. 2
• Do not administer Lantus intravenously or via insulin pump. 2
• Avoid injecting into areas of lipodystrophy, and rotate injection sites within the same region. 2

Alternative Consideration

If the goal is to maintain a simpler twice-daily regimen rather than moving to basal-bolus therapy, consider that premixed insulin formulations are not routinely recommended in hospital settings due to increased hypoglycemia risk. 1 However, the 2025 ADA guidelines support basal-bolus regimens as preferred treatment for patients with good nutritional intake, making the Lantus plus rapid-acting insulin approach the superior choice for most patients. 1

Clinical Advantages of This Switch

Lantus provides more predictable basal insulin coverage with reduced nocturnal hypoglycemia risk compared to NPH-containing insulins like 70/30. 4, 8 Studies demonstrate a 26% reduction in nocturnal hypoglycemia and 46% reduction in severe hypoglycemia with insulin glargine versus NPH insulin, while achieving equivalent glycemic control. 8 This allows more aggressive titration toward HbA1c targets with greater safety. 8