Freeze-drying in one paragraph
The FDA’s guide to inspecting lyophilization describes it as a process that takes water out of a product after the product has been frozen and placed under a vacuum. In those conditions ice changes straight into vapour without becoming liquid first. The guide splits the process into three linked stages: freezing, primary drying, in which ice is removed by sublimation, and secondary drying, in which remaining water is driven off by desorption [1].
What is left in the vial is a dry, porous solid. The guide calls it the cake, and its volume and appearance are part of what manufacturers inspect [1].
Why make a medicine this way
The guide is direct about the reason: products are made in lyophilized form because they are unstable in solution. Among its examples are several antibiotics and many biotechnology-derived products [1].
- Advantages listed by the FDA: better stability as a dry powder, water removed without heating the product too much, a liquid that is easier to handle aseptically during manufacture, and quick, easy dissolving when the product is reconstituted [1].
- Disadvantages listed by the FDA: more handling and processing time, the need for a sterile diluent at reconstitution, and costly, complex equipment [1].
How the vials are made
The guide outlines the usual steps. The drug and other ingredients are dissolved, generally in water for injection, and the solution is sterilised by passing it through a 0.22-micron filter that holds back bacteria. It is filled into sterile vials, which are only partly stoppered, then frozen on cooled shelves inside the freeze-dryer. A vacuum is applied and the shelves are warmed so the frozen water evaporates, and finally the stoppers are pushed fully home inside the chamber [1].
Because the vials stay open until that last step, the guide stresses that filling, transport and loading must happen under aseptic conditions [1]. A sterile powder depends on a clean process, not on anything you can see in the vial.
Three approved peptide powders
Gattex® contains teduglutide, a 33-amino-acid analogue of GLP-2. Its label describes a single-dose glass vial of white lyophilized powder, with mannitol, L-histidine and sodium phosphates as the other ingredients and no preservatives [2].
Tesamorelin, a 44-amino-acid peptide, comes in two US products. Egrifta SV® is a preservative-free, white to off-white powder in a single-dose vial, with histidine, mannitol, polysorbate 20 and sucrose as inactive ingredients, mixed with sterile water [3]. Egrifta WR™, approved in 2025, is also a preservative-free white to off-white powder, with hydroxypropyl betadex and mannitol, in a single-patient-use vial; its diluent is bacteriostatic water, which contains benzyl alcohol as a preservative [4]. The label states that the two formulations differ in reconstitution and storage and are not substitutable [4].
Storage: powder and solution are different
A powder can often be stored more simply than a solution, but each label sets its own conditions. The table puts the powder and the mixed solution side by side.
| Product | Powder before mixing | After mixing |
|---|---|---|
| Gattex® | Refrigerated at 2–8°C until dispensed; then kept at room temperature up to 25°C with a 90-day use-by date; do not freeze [2] | Inject within 3 hours; do not shake or freeze; discard what is left [2] |
| Egrifta SV® | Room temperature, 20–25°C, in the original box to protect it from light [3] | Inject straight away; do not store, refrigerate or freeze [3] |
| Egrifta WR™ | Room temperature, 20–25°C, in the original box to protect it from light; do not freeze [4] | Room temperature; discard 7 days after mixing; do not freeze [4] |
What the storage rows tell you
Two points stand out. First, “room temperature” is a defined range on these labels, not any warm cupboard, and the tesamorelin labels add light protection by keeping vials in their box [3][4]. Second, the stability that freeze-drying gives belongs to the dry powder, not to what you make from it: two of the three solutions are used within hours, and the third has a fixed seven-day limit [2][3][4].
The labels also differ on freezing. Gattex® says not to freeze the vials, and Egrifta WR™ says not to freeze either the powder or the solution, while the Egrifta SV® label gives the freezing instruction only for the mixed solution [2][3][4]. Where a label is silent, the safe source for an answer is the pharmacist, not a rule borrowed from another product.
What can go wrong, and what you can check
The FDA guide describes a defect called meltback, a collapse of the cake caused by incomplete sublimation, which can leave a pocket of moisture and make the product less stable. It also notes that moisture content is tested against limits, and that a product which dissolves slowly may lose some potency if it is not fully dissolved [1].
Those checks belong to the manufacturer. Your reference is the label: the description of the powder and of the mixed solution, and the storage conditions. The Egrifta WR™ instructions ask you to look at the powder before mixing and not to use a vial whose powder is discoloured or contains particles [4]. The Gattex® label says not to use the product if it has not dissolved after a second attempt, and to discard a solution that is discoloured or contains particles [2]. MedlinePlus adds the general steps of checking the label, the date and the appearance of any vial, and asking for the instructions when a powder has to be mixed [6]. If something does not match the label, ask your pharmacist before using it.
Powders without a label
A powder vial may also reach you without an approved label at all. The FDA has warned companies that illegally sold semaglutide, tirzepatide, retatrutide, survodutide or mazdutide falsely labelled “for research purposes” or “not for human consumption” directly to consumers with dosing instructions, and it calls such products of unknown quality and possibly harmful [5].
Without an approved label there is no reviewed description of the powder, its storage, its diluent or how long it lasts after mixing. None of the checks above can be done against a document that does not exist, which is one practical reason the FDA urges consumers not to buy these products [5].
What to note for a powder you use
Useful facts are the product and strength, the lot number and expiry, how it is stored, the diluent added and the date and time of mixing. With those, a pharmacist can answer most questions about a vial.
If a kit uses one diluent bottle for several mixes, its first-use date matters too; the Egrifta WR™ instructions ask you to record it and to discard the bottle 28 days after first use [4].
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.