The word in plain terms
To reconstitute a medicine is to turn a dry powder back into a liquid by adding a measured amount of a sterile liquid. Many such powders are made by freeze-drying, which removes water from a solution; reconstitution puts liquid back [4].
The FDA’s guide to freeze-dried injectables lists quick, easy dissolving as one advantage of these products and the need for a sterile diluent at reconstitution as one disadvantage [4]. The CDC notes that the US Pharmacopeia’s sterile compounding standard, USP chapter 797, includes reconstituting in its definition of sterile compounding, alongside diluting, combining and repackaging [5].
Three approved labels side by side
Gattex® (teduglutide) is a 33-amino-acid peptide used for short bowel syndrome in adults and in children from 1 year of age who depend on parenteral support. It comes as a single-dose vial of white freeze-dried powder with sterile water in a prefilled syringe [1]. Tesamorelin, a 44-amino-acid peptide, is sold in the US as two separate products: Egrifta SV®, a single-dose vial mixed with sterile water, and Egrifta WR™, approved in 2025, a single-patient-use vial mixed with bacteriostatic water that supplies a week of daily doses [2][3].
The table compares only the handling steps. The amounts of powder and liquid are deliberately left out: they differ between products, and the label for your own product is the only place to take them from.
| Product | Diluent named in the label | How to mix | After mixing |
|---|---|---|---|
| Gattex® | Preservative-free sterile water, in the kit [1] | Push the water in slowly, let stand, roll between the palms, let stand again; do not shake [1] | Inject within 3 hours; do not shake or freeze; discard the rest [1] |
| Egrifta SV® | Only the sterile water supplied [2] | Aim the water down the inside wall of the vial to avoid foaming, then roll gently; do not shake [2] | Inject straight away; do not store, refrigerate or freeze the solution [2] |
| Egrifta WR™ | Only the bacteriostatic water supplied [3] | Swirl the vial in a circle, then wait a few seconds for the foam to settle; do not shake [3] | Keep at room temperature; discard 7 days after mixing; do not freeze [3] |
The diluent is part of the instructions
The label tells you which liquid to use, and the choice is not interchangeable. The Egrifta SV® label says to use only the sterile water provided, the Gattex® label specifies the preservative-free sterile water in the kit, and the Egrifta WR™ label names only the bacteriostatic water that comes with it [1][2][3]. The same molecule can therefore be paired with different liquids in different products.
Diluents differ in what they contain. Sterile water for injection has no preservative. Bacteriostatic water contains benzyl alcohol to hold back bacteria, and its own label says it is not for use in newborns and that some drugs are incompatible with benzyl alcohol, with a pharmacist as the person to consult [6]. In a passage on sterility testing, the FDA’s freeze-drying guide also remarks that many hospitals use only plain water for injection because of potential toxicities of bacteriostatic water [4]. If your product or prescription does not name a diluent, that is a question for your pharmacist before the first mix.
How the labels say to mix
- Start clean. The Egrifta WR™ instructions begin with washing and drying your hands and wiping the tops of the vial and the water bottle with an alcohol swab; MedlinePlus gives the same first steps for any vial [3][7].
- Check the dates. The Egrifta WR™ instructions ask you to check the expiry on both the powder vial and the water bottle, and not to use either if it has expired [3].
- Add the liquid gently. Gattex® has you push the water in slowly, and Egrifta SV® directs it down the side of the vial rather than onto the powder [1][2].
- Roll or swirl, never shake. Gattex® uses a sequence of standing and rolling, Egrifta SV® gentle rolling, Egrifta WR™ swirling followed by a short rest [1][2][3].
- Make sure it has dissolved. If powder remains, Gattex® allows another gentle roll and says not to use the product if it is still not dissolved after a second try [1].
- Use the supplied needles and syringes for each step, as each kit describes, and put used ones straight into a sharps container [1][2][3].
Look before you draw it up
Each label asks you to inspect the mixed solution. Gattex® should be clear and colourless to light straw-coloured, with no particles; if it is discoloured or contains particles, it is thrown away. Egrifta SV® and Egrifta WR™ are used only if the solution is clear and colourless and free of particles [1][2][3]. The Egrifta WR™ instructions add a look at the powder itself before mixing: it should be white to off-white, and a discoloured powder or one with particles is not used [3].
MedlinePlus lists the same kinds of change to watch for in any vial: a different colour, small floating pieces or cloudiness [7]. Complete dissolving matters too. The FDA guide warns that when a freeze-dried product takes longer to dissolve, part of its potency may be lost if it is not fully dissolved [4]. A cloudy vial or floating particles are a reason to stop and ask, not to mix harder.
The clock starts when you mix
A powder can be stable for a long time; a mixed solution often is not. The Gattex® label says to inject within 3 hours of mixing and to discard what is left. The Egrifta SV® label says to inject right after mixing and not to keep, refrigerate or freeze the solution. Egrifta WR™ is the exception that shows why the label matters: one mixed vial is kept at room temperature for 7 days of daily doses and then discarded, whatever is left [1][2][3].
The CDC gives the general principle for clinics: preparing an injection as close as possible to the time it is given protects both its sterility and its stability [5]. It also notes that creating a batch of pre-drawn syringes may count as pharmaceutical compounding, and that where pre-filled syringes are needed, the options it names are syringes made by a manufacturer or by an FDA-registered outsourcing facility [5]. Products meant for several doses from one vial follow their own rules, covered in the article on multi-dose vials.
Why the numbers stay with your label
The volume of diluent sets the strength of the solution, so the same powder mixed with a different volume gives a different amount of medicine at each syringe mark. That is why every label fixes both the liquid and how much of it, and why the tesamorelin labels warn that their two products cannot be substituted for one another [3].
This article therefore gives no example calculation. Your prescriber or the product label sets the dose, and the label sets the diluent volume. If the instructions you were given do not state the volume to add or the volume to draw, or if they disagree with the label, ask your pharmacist before the first injection.
What to write down
For a powder you mix yourself, the useful facts are the product and strength, the diluent, the date and time you mixed it, and when you injected. For a kit with a shared diluent bottle, the date the bottle was first opened matters as well: the Egrifta WR™ instructions ask you to record it, discard the bottle 28 days after first use, and supply a mixing and injection tracker for the purpose [3].
If something does not look right, these details answer most of the questions a pharmacist will ask.
Gattex® is a registered trademark of Takeda Pharmaceuticals U.S.A., Inc. Egrifta SV® is a registered trademark and Egrifta WR™ is a trademark of Theratechnologies Inc. PepLabo is not affiliated with or endorsed by Takeda or Theratechnologies.
