In a patient on basal‑bolus insulin and tirzepatide, should insulin be titrated by increasing or decreasing the basal dose by 2 units (and the bolus dose by 1‑2 units) based on glucose readings?

Insulin Titration: Increase by 2 Units for Basal, 1-2 Units for Bolus

Yes, insulin should be titrated by increasing basal insulin by 2 units every 3 days to reach fasting plasma glucose goals, and bolus insulin should be increased by 1-2 units or 10-15% of the current dose when adjusting prandial coverage. 1

Basal Insulin Titration Algorithm

The 2025 American Diabetes Association Standards of Care provides explicit guidance on basal insulin titration 1:

• Increase by 2 units every 3 days until fasting plasma glucose goal is achieved without hypoglycemia
• This is described as an "evidence-based titration algorithm" in the guidelines
• For hypoglycemia without clear cause: decrease dose by 10-20% (not by 2 units—use percentage reduction)

Bolus (Prandial) Insulin Titration

When adding or adjusting prandial insulin 1:

• Start with 4 units per day OR 10% of basal insulin dose
• Increase by 1-2 units OR 10-15% of current insulin dose based on postprandial glucose readings
• For hypoglycemia: decrease corresponding dose by 10-20%

Special Consideration: Tirzepatide Co-Administration

Critical caveat: When tirzepatide is being used concurrently with basal-bolus insulin, you need to proactively reduce insulin doses to prevent hypoglycemia, not increase them 2, 3, 4:

• Recommend reducing total daily insulin by 25% at tirzepatide initiation in patients with baseline A1C <7.5% 2
• Expect median insulin reduction of approximately 9-10% within 6 months of adding tirzepatide 3
• Patients with baseline A1C ≤8.0% require larger insulin reductions (-22.6%) compared to those with higher A1C 3
• In type 1 diabetes studies, tirzepatide reduced total daily insulin by 24.2 units/day (35% reduction) 4

Practical Algorithm for Patients on Tirzepatide + Insulin

1. Before starting tirzepatide: Reduce total daily insulin by 25% if A1C <7.5%
2. Monitor closely: Most insulin reduction occurs within first 2 months 2
3. If glucose remains elevated: Use the standard 2-unit basal increase every 3 days, but expect smaller total insulin requirements
4. Watch for hypoglycemia: 12% incidence reported when transitioning from GLP-1 RA to tirzepatide 3

Common Pitfalls

• Don't use 2-unit increments for dose reductions in hypoglycemia—use 10-20% reductions instead, as this is more physiologically appropriate
• Don't continue aggressive insulin titration when adding tirzepatide—the incretin effect will substantially reduce insulin needs
• Don't forget to reduce basal insulin (by 4 units/day or 10%) when A1C <8% before adding prandial insulin 1

The 2-unit increment for basal insulin increases is well-established and evidence-based, but the context of concurrent tirzepatide therapy fundamentally changes the approach from dose escalation to dose reduction.