Reconstitution

Lyophilised peptide arrives as a dry cake or powder under vacuum. Reconstitution is the act of dissolving that cake into a known volume of sterile diluent so that a measurable fraction of it can be withdrawn.

Choosing a diluent

Bacteriostatic water is sterile water containing roughly 0.9% benzyl alcohol, which suppresses microbial growth and makes multi-draw vials viable for a matter of weeks under refrigeration. Sterile water for injection contains no preservative and is generally reserved for single-draw work. A handful of compounds — copper peptides and some acetate salts among them — have documented compatibility quirks with benzyl alcohol, so check the compound profile before defaulting.

The mechanics

1. Let the vial reach room temperature before opening. Cold glass plus cold powder makes for slow, incomplete dissolution.
2. Swab both stoppers with isopropyl alcohol and let them dry.
3. Draw the diluent, then angle the needle so the stream runs down the inner wall of the vial rather than jetting directly onto the cake. Peptide bonds are mechanically fragile.
4. Let the vacuum pull the diluent in; don't force the plunger.
5. Swirl gently or let it sit. Never shake. Agitation shears peptide chains and denatures them.
6. Wait until the solution is completely clear. Persistent cloudiness or visible particulate after several minutes means something is wrong — don't proceed.

The arithmetic

The diluent volume is a free choice, and it is the only lever you have over measurement precision. A 5 mg vial in 1 mL gives 5 mg/mL, which puts a 250 mcg dose at 5 units — legible, but every half-unit of error is a 10% dosing error. The same vial in 2.5 mL gives 2 mg/mL and puts that dose at 12.5 units, where the same absolute error matters far less. Dilute enough that your target lands somewhere in the mid-range of the barrel.

Syringes & Units

An insulin syringe marked U-100 is calibrated for insulin at 100 international units per millilitre. That calibration is what defines the unit: 1 unit = 0.01 mL. This holds regardless of barrel size — a 0.3 mL barrel simply stops at 30 units, a 0.5 mL at 50, a 1 mL at 100.

This is the single most common source of error in peptide work. A "unit" is a volume, not a quantity of peptide. Ten units of a 2 mg/mL solution and ten units of a 10 mg/mL solution are the same volume and five times different in content.

The unit chain

Four units of measure show up constantly and they are not interchangeable:

• mg — milligram. Mass. What vials are labelled in.
• mcg (µg) — microgram. 1 mg = 1000 mcg. What most non-GLP-1 research doses are expressed in.
• IU — international unit. A biological activity measure, not a mass. Conversion to mg is compound-specific: growth hormone is conventionally ~3 IU per mg, hCG is a different scale entirely. Never assume a universal factor.
• Syringe units — pure volume. 1 unit = 0.01 mL. Meaningless without knowing the concentration.

Storage & Stability

Lyophilised peptide is comparatively robust: kept dry, dark, and at −20 °C, most compounds in this database are stable for a year or more, and many tolerate 2–8 °C for months. The moment water is introduced, that changes.

Practical points

• Do not freeze a reconstituted vial. Ice crystal formation and repeated freeze–thaw cycles are among the most destructive things you can do to a peptide in solution.
• Copper peptides (GHK-Cu) and several others are photosensitive. Amber vials or foil, not a clear vial on a shelf.
• Store vials upright, away from the fridge door where temperature swings are largest.
• Date the vial at reconstitution. Memory is not a stability record.
• Cloudiness, colour change, or visible particulate that develops after a clear reconstitution means the solution has failed. Discard it.