Leftover tirzepatide in a vial is usually a sizing question, not a storage one. FDA recommends using a compounded multi-dose vial within 28 days of first use[2]. After that, it says to discard it, even if medicine remains[2].
Tirzepatide is injected once a week[1]. So a vial gets four doses before the 28-day mark. The leftover is the vial’s milligrams minus those four doses. The milligrams a 28-day vial should hold at each dose are tabled in how long a vial of tirzepatide lasts.
Where the dose steps come from
The Zepbound label starts at 2.5 mg once weekly for 4 weeks[1]. It then raises the dose in 2.5 mg steps, each after at least 4 weeks[1]. Maintenance is 5 mg, 10 mg or 15 mg for weight reduction[1].
So a step can land anywhere in a compounded vial’s life. It depends on when the vial was opened. The prescriber sets the step. The arithmetic below only follows it.
Five example vials, worked
The vial sizes here are round examples, not any pharmacy’s product. Each row runs four weekly doses, then discards the rest at day 28.
| Vial and schedule | Used | Discarded at day 28 |
|---|---|---|
| 10 mg vial: four weeks at 2.5 mg | 10 mg | 0 mg (0%) |
| 20 mg vial: four weeks at 2.5 mg | 10 mg | 10 mg (50%) |
| 20 mg vial: two at 2.5 mg, then 5 mg | 15 mg | 5 mg (25%) |
| 20 mg vial: four weeks at 5 mg | 20 mg | 0 mg (0%) |
| 10 mg vial: two at 2.5 mg, then 5 mg | 10 mg; runs dry, 1 dose short | 0 mg (0%) |
Row one is the clean case: a 10 mg vial at 2.5 mg empties in four doses. Nothing is left, so 0% is discarded.
Row two is the costly one. A 20 mg vial at 2.5 mg uses 10 mg. The other 10 mg is discarded. The price per milligram actually used is 2 times the vial’s nominal rate.
Row three steps up to 5 mg after two doses. The same vial now uses 15 mg. Only 5 mg is discarded, or 25%. The increase cut the waste.
The opposite problem: running dry
Row five is a 10 mg vial with the same step. Two doses of 2.5 mg and one of 5 mg use all 10 mg. The fourth dose has nothing to draw from.
That is a refill a week early. On a plan billed every four weeks, the next charge still lands on its usual date. The gap is a timing cost, not a price cost. How four-week billing lines up with a calendar is in billed every 4 weeks vs monthly.
Brand vials and pens: one strength, then discard
Brand Zepbound avoids the mid-vial question by design. Each multi-dose vial and KwikPen holds four doses of one strength[1]. A step up means the next strength, in a new vial or pen.
The label says to throw away an opened multi-dose vial or KwikPen after 4 weekly doses[1]. The same applies after 30 days from first use, even with medicine left[1].
The KwikPen instructions are blunter. They say not to inject the leftover medicine[1]. They also say not to move it from the pen into a syringe[1]. An opened single-dose vial is thrown away after use, even if medicine is left[1].
Four doses per presentation, and at least four weeks per step, line up. On the label schedule, one multi-dose vial or pen covers one step.
What to ask before the vial ships
- How many milligrams the vial holds in total.
- Whether that total matches four doses at the current dose, or the next one.
- What happens to the refill date if the dose steps up mid-vial.
Reading a dose off the syringe is covered in how many units is 2.5 mg of tirzepatide. Compare vials by price per milligram used on the cost-per-milligram calculator. The monthly market is in the tirzepatide cost guide.