Mixing a powder with sterile water

General information about the equipment, not medical advice. The directions that came with your medicine and the person who prescribed it come first, every time.

What we do and do not supply

We sell bacteriostatic water, sterile water for injection, vial adapters, drawing-up needles, syringes and swabs. We do not sell peptides, hormones or any prescription medicine, in any form, and we are not going to tell you what to put in the vial or how much of it to use.

This page is about the equipment and the arithmetic. Everything specific to a compound comes from whoever is managing your treatment.

Bacteriostatic water and sterile water are different

Sterile water for injection is exactly that and nothing else. Once you pierce the stopper it is a single use product, because there is nothing in it to stop bacteria growing.

Bacteriostatic water contains benzyl alcohol, usually around nine tenths of a per cent, which inhibits bacterial growth and allows a vial to be entered more than once over a period of days. That is what makes a multi-dose vial practical.

Benzyl alcohol is not suitable for everyone, and which diluent is right is part of the prescribing decision rather than a preference.

The volume you add sets the concentration

This is the part people get wrong. The powder is a fixed amount. The liquid you add is what changes, and it determines how much powder ends up in each unit on the syringe.

Put simply: add twice as much water and every mark on the barrel is worth half as much. Nothing about the powder changed. Which is why the volume has to be the one you were told to use, and why writing it on the vial matters.

Our reconstitution calculator does the arithmetic if you have the strength and the volume. It does not tell you what either of them should be.

What the benzyl alcohol is actually doing

Bacteriostatic water is sterile water with roughly 0.9 per cent benzyl alcohol in it, and bacteriostatic is the precise word: it inhibits bacterial growth rather than killing what is already there. It is a preservative, not a steriliser, and it is the entire difference between the two products.

That preservative is why a vial can be entered more than once. Sterile water for injection has nothing in it to stop something growing, so the moment the stopper is punctured the clock is short and the vial is a single use item in practice whatever its volume.

Nothing in either of them treats anything. They are diluents, which is to say they are the liquid and not the point.

Vial sizes, and how long an opened one is good for

Bacteriostatic water is commonly sold in 10mL, 20mL and 30mL glass vials. The size to buy is the one you will finish, because the useful life of an opened vial is set by the date on it and by how many times it has been entered, not by how much is left in it.

Read the vial for that figure rather than a general rule, and it is usually shorter than people assume. Write the date you first punctured it on the label, because that is the number you will want later and will not remember.

Store it as the carton says, which for these is room temperature and out of light. Storing supplies covers the rest of the drawer, and a vial that has spent an afternoon in a hot car is not the vial you think it is.

Keeping the vial clean

Swab the stopper before every entry and let it dry. Every time, not just the first.

Add the water slowly, down the inside wall of the vial rather than straight onto the powder. Then swirl or roll it gently until it dissolves. Do not shake it. Many of these compounds are fragile and shaking is what foams and damages them.

A vial adapter seats once in the stopper and gives you a clean luer port to work through, which means you are not pushing a needle through the same piece of rubber over and over. On a vial you will enter many times it pays for itself in coring alone.

Label it. Date, what is in it, and the volume you added. In a month you will not remember, and guessing is not an option.

Two needles make this easier than one: a wide blunt one to draw with and a fine one to inject with. Both are in syringes and needles, alongside the bacteriostatic water and swabs that go with them.

The three of them side by side