No, Lantus and Novolog 70/30 Should Not Be Used Together
You should use either basal insulin (Lantus) with rapid-acting insulin (regular insulin aspart, not the 70/30 mix) OR switch entirely to premixed insulin (Novolog 70/30), but not combine both regimens. This is a fundamental principle of insulin therapy design—these represent two different treatment strategies that should not be mixed 1.
Why This Combination Doesn't Make Sense
Understanding the Insulin Types
- Lantus (insulin glargine): A long-acting basal insulin providing 24-hour background insulin coverage
- Novolog 70/30: A premixed insulin containing 70% intermediate-acting insulin aspart protamine and 30% rapid-acting insulin aspart—this already provides BOTH basal and prandial coverage in one injection
The core problem: Using both together means you're essentially doubling up on basal insulin coverage, which creates unnecessary complexity, increases hypoglycemia risk, and makes dose adjustments extremely difficult.
What the Guidelines Actually Recommend
The 2017-2018 ADA guidelines clearly outline that when basal insulin alone (like Lantus) fails to achieve glycemic targets, you have distinct options 1:
Option 1: Add prandial insulin to basal
- Continue Lantus
- Add rapid-acting insulin aspart (NOT the 70/30 mix) before the largest meal or multiple meals
- This creates a basal-bolus regimen
Option 2: Switch to premixed insulin
- STOP basal insulin (discontinue Lantus)
- START twice-daily premixed insulin like Novolog 70/30 before breakfast and dinner 1
The guidelines explicitly state: "stopping basal insulin and starting twice-daily premixed (or biphasic) insulin" 1—note the word "stopping."
The Correct Clinical Approach
If Currently on Lantus Alone and Need Intensification:
First choice: Add single injection of rapid-acting insulin aspart (the regular formulation, not 70/30) before the largest meal while continuing Lantus 1, 2
Alternative: Stop Lantus entirely and switch to Novolog 70/30 twice daily (before breakfast and dinner) 1
If Already Using Both (Medication Error Scenario):
This likely represents a prescribing error or misunderstanding. You need to:
- Assess current glycemic control with glucose monitoring
- Choose ONE strategy:
- Basal-bolus: Continue Lantus + switch Novolog 70/30 to regular rapid-acting insulin aspart before meals
- Premixed: Discontinue Lantus + continue Novolog 70/30 twice daily
Critical Safety Concerns
Hypoglycemia risk: Combining these insulins creates overlapping insulin action profiles that significantly increase hypoglycemia risk, particularly overnight when both the basal component of the 70/30 and Lantus are active simultaneously.
Dose titration impossibility: You cannot properly adjust doses when using both—if blood sugars are high, which insulin do you increase? The overlapping pharmacodynamics make rational dose adjustments nearly impossible.
FDA labeling: The Lantus label explicitly states "LANTUS must NOT be diluted or mixed with any other insulin or solution" 3. While this primarily refers to physical mixing in the same syringe, the principle extends to avoiding unnecessarily complex regimens that combine different insulin strategies.
Common Clinical Pitfall
This combination sometimes occurs when providers try to "add on" to existing therapy without fully transitioning the regimen. The 2018 ADA guidelines specifically warn against "unnecessarily complex or costly regimens" 2. Using both Lantus and Novolog 70/30 simultaneously falls squarely into this category.
The evidence shows these regimens are alternatives to each other, not complementary therapies 1. Studies comparing basal insulin plus rapid-acting insulin versus twice-daily premixed insulins show noninferiority—they achieve similar outcomes through different mechanisms, reinforcing that you choose one approach or the other 1.