Insulin product conversion
Convert between insulin products, applying the recognised 80% adjustments for NPH to glargine and for Toujeo to other glargine products.
What is this for?
Most insulin products interchange approximately unit for unit, but two situations require a dose reduction. Converting twice-daily NPH to once-daily glargine uses 80% of the NPH total daily dose, and converting from Toujeo (U-300 glargine) to another glargine product uses 80% of the Toujeo dose because Toujeo has lower relative bioavailability.
How to use it
- Select the conversion scenario. Only the two listed exceptions carry a dose reduction; everything else is unit for unit.
- Enter the total daily dose, summing all injections of the current product.
- Round the result to a dose the patient's device can actually deliver, and arrange close follow-up.
Worked example
A patient takes NPH insulin 24 units in the morning and 16 units in the evening, a total of 40 units daily. Convert to once-daily glargine.
Answer: 40 × 0.8 = 32 units of glargine once daily. The reduction reflects glargine's flatter, longer profile and reduces the risk of nocturnal hypoglycaemia during the switch.
Clinical pearls & pitfalls
- The 80% reduction applies when NPH is given twice daily. Converting once-daily NPH to glargine is generally unit for unit.
- The Toujeo reduction runs in one direction. Going from Toujeo to another glargine uses 80%; going the other way, from glargine to Toujeo, is generally unit for unit and often requires a subsequent dose increase.
- Basal insulin conversion does not change prandial insulin. If the patient is on a basal-bolus regimen, the mealtime doses are converted separately.
- Concentrated insulins are a recognised source of serious error. U-500 insulin is five times as concentrated as U-100, and a syringe mix-up is a five-fold overdose.
- Insulin is on the ISMP high-alert list. Independent double-checking of any conversion is standard practice in most institutions.
Assumptions & limitations
- Provides a starting dose only. Every insulin conversion requires individualised titration against glucose readings.
- Does not account for renal impairment, which reduces insulin clearance and typically requires lower doses.
- Does not cover conversion between insulin and non-insulin therapies, or between premixed and separate-component regimens, both of which require clinical assessment rather than a factor.
- Does not address the timing changes that accompany a switch, which can matter as much as the dose.
References
- American Diabetes Association Professional Practice Committee. Standards of Care in Diabetes — 2025. Diabetes Care. 2025;48(Suppl 1).
- Product labelling for insulin glargine (Lantus, Basaglar, Semglee), insulin glargine U-300 (Toujeo), and NPH insulin.
- Institute for Safe Medication Practices. ISMP List of High-Alert Medications in Acute Care Settings.