Toujeo Dose Calculator
Estimate a starting dose of insulin glargine U-300 — and understand the two things that make Toujeo behave differently from Lantus despite being the same molecule.
💎 Toujeo Starting Dose
Same molecule, different behaviour
Toujeo is insulin glargine — chemically the same as Lantus — formulated at U-300, three times the concentration. That single change alters how it behaves, because a more concentrated depot under the skin has a smaller surface area relative to its volume and therefore dissolves more slowly.
The result is a profile that is flatter and longer: onset over roughly 6 hours, no peak, and duration up to 36 hours against Lantus’s 24. In practice that means more stable overnight coverage and more forgiveness if an injection is late.
| Lantus (U-100) | Toujeo (U-300) | |
|---|---|---|
| Concentration | 100 units/mL | 300 units/mL |
| Onset | 1–2 hours | ~6 hours |
| Duration | ~24 hours | up to 36 hours |
| Time to steady state | 2–3 days | ~5 days |
| Pen capacity | 300 units (3 mL) | 450 units (1.5 mL) |
| In-use window | 28 days | 56 days |
The five-day rule
This is the practical point that catches people out. Toujeo takes around five days to reach full pharmacodynamic steady state, considerably longer than U-100 glargine.
Someone who starts Toujeo and finds fasting glucose still high on day two has not learned that the dose is too low — they have learned that the insulin has not finished arriving. Increasing at that point stacks a change on top of an effect still building, and the low tends to appear several days later when both have landed.
So titrate no faster than every three to five days, and expect the first week to look worse than the second on an unchanged dose. The same applies in reverse when reducing.
Switching to or from Toujeo
Because the pen dials in units rather than volume, switching does not require any arithmetic on the patient’s part — you dial the number you are told. But the products are not equivalent unit-for-unit in effect, and the direction matters.
Moving from a U-100 basal to Toujeo, many patients need a somewhat higher unit dose to achieve the same fasting control. Moving the other way, from Toujeo to a U-100 basal, a dose reduction is usually needed to avoid hypoglycemia. Either direction is a prescriber-led change with closer monitoring for the first week or two — which, given the five-day steady state, is exactly how long it takes to see what the change actually did.
Limitations & Safety Notes
- Toujeo takes about five days to reach steady state. Titrating faster than every 3–5 days means reacting to an effect that has not fully appeared.
- Switching between Toujeo and any U-100 basal is not a unit-for-unit swap. Dose adjustment and closer monitoring are needed in both directions.
- Never draw Toujeo into a syringe from the pen. At U-300, a syringe marked for U-100 would deliver three times the intended dose.
- A high fasting reading may be dawn phenomenon or rebound rather than insufficient basal. Raising the dose in those cases risks nocturnal hypoglycemia.
- Starting doses are published ranges. Actual requirement is settled by titration under prescriber supervision.
Frequently Asked Questions
Is Toujeo stronger than Lantus?
It is more concentrated, not more potent per unit. Toujeo is U-300, three times the concentration of Lantus at U-100, which changes how the depot absorbs — flatter and longer — rather than making each unit do more work.
How do I switch from Lantus to Toujeo?
It is a prescriber decision. Because the pen dials in units, you dial the number you are given — but many patients need a somewhat higher unit dose on Toujeo to reach the same fasting control, and the reverse switch usually needs a reduction.
How long does Toujeo take to work?
Onset is over about 6 hours, but the more important figure is that full steady state takes around five days. Judging a dose before then means judging an effect that is still building.
How often should I titrate Toujeo?
No faster than every 3 to 5 days, because of the five-day steady state. The usual step is 2 units against fasting glucose.
Can I use a syringe with Toujeo?
No. The pen must be used as supplied. At U-300, drawing it into a U-100 syringe would deliver three times the intended dose — a serious overdose risk.
How long does an opened Toujeo pen last?
56 days at room temperature, twice the 28-day window of most U-100 basals. Discarding it at 28 days out of habit throws away four usable weeks.
Sources
- American Diabetes Association. 9. Pharmacologic Approaches to Glycemic Treatment: Standards of Care in Diabetes — 2026. Diabetes Care. 2026;49(Suppl 1):S183. Link — basal initiation and titration principles
- Sanofi. Toujeo (insulin glargine injection) 300 Units/mL — dosing information. Link — concentration, profile and titration
- Endotext / NCBI Bookshelf. Inpatient Diabetes Management. Link — weight-based basal dosing ranges
Last reviewed: July 2026