Mixing (reconstituting) a vial, step by step

Reconstituting a vial means adding bacteriostatic water to a freeze-dried powder. It takes a handful of steps and about five minutes, and the two mistakes that ruin it are shaking instead of swirling, and injecting with the mixing needle. Here is the whole procedure, with the supplies each step needs.

Last edited 2026-09-28 · written by PepPrep · not medical advice

This is the standard technique, described in terms of the supplies involved:

1. Set up clean. Wash hands, put on gloves if you use them, and wipe the work surface with 70% alcohol.
2. Swab both stoppers. One alcohol pad for the water vial's rubber top, a fresh one for the powder vial's. Let them air-dry a few seconds.
3. Draw the water. Use a luer-lock syringe (a blunt fill needle makes this quick) and pull up your chosen amount — the calculator helps you pick a convenient one (luer-lock syringes are marked in mL; 3 mL covers most amounts, a 10 mL one anything larger).
4. Add it slowly, down the glass. Angle the needle so water runs down the inside wall of the powder vial instead of jetting onto the powder.
5. Swirl, never shake. Gently roll or swirl until the liquid is clear. Shaking is the classic beginner mistake — delicate contents don't appreciate it.
6. Label it. Write the date and how much water went in (e.g. "mixed 29 Aug, 2 mL") on tape or the label. Future-you will be grateful.
7. Store it cold and dark, and put used needles in a sharps container — never household trash.

Two things worth doing before you start

Let a cold vial come up to room temperature. Going straight from the fridge means the contents dissolve more slowly and the glass fogs with condensation, which is a nuisance exactly when you are trying to read a label. Twenty minutes on the counter covers it. This is ordinary handling of cold glass — if what you have came with its own instructions, those win over any rule of thumb here.

Expect the vial to pull. Freeze-dried vials are often sealed under a partial vacuum, so the moment the needle is through the stopper the liquid starts drawing itself in and you barely have to push. That is normal, not a fault. If yours does not pull, push slowly rather than forcing it — the aim is still to run the liquid down the inside wall rather than jetting it straight at the powder.

What usually goes wrong

• Do not shake it. A common mistake, and swirling is slower on purpose. If you end up with a head of foam on top, that is what shaking looks like — set it down and leave it alone until it settles.
• Do not rush it. Some contents take several minutes to go clear by themselves. Waiting is doing something, and it is the part people skip.
• Let the stopper dry before you puncture it. Alcohol needs a few seconds of air-drying to do its job. Swabbing and puncturing in the same movement wastes the swab entirely.
• Do not inject with the mixing needle. An 18G blunt fill needle is for moving liquid between vials and nothing else. Blunt makes it far less likely to stick you while you draw, but it is still a sharp: it will go through skin under force, and it goes in the sharps container like any other needle. Swap to a fresh fine needle or an insulin syringe for the injection itself.
• Do not core the stopper. A thick needle pushed straight down through the same spot again and again can cut a tiny plug out of the rubber, which ends up floating in the vial. Go in at a slight angle with the bevel up, use a fresh spot each time, or use a vial adapter, which is made to seat once and stay put.
• Do not leave it unlabelled. Two unlabelled vials in a fridge are indistinguishable a fortnight later. Write on it before it goes away, not afterwards.

If it will not go clear at all, stop. Do not warm it up to hurry it along, and read the cloudy-vial guide before you do anything else, including adding more liquid. Check the instructions that came with it, because what is actually in the vial is not something a shopping guide can see from here.

Supplies mentioned: water & vials · syringes · alcohol pads, gloves, sharps

Check your product's label: DailyMed (opens in a new tab) in the US; official sources for other countries.

Equipment only: nothing on this page is advice about what to inject, how much, or whether a product is fit to use. That comes from the product's labelling and whoever supplied it.