Work out the concentration before you touch anything
Reconstitution is one division: vial strength ÷ diluent volume = concentration. A
10 mg vial in 2 mL is 5 mg/mL, which on a U-100 insulin syringe is 50 mcg per unit.
Everything downstream follows from that one number.
The diluent volume is a free choice, and choosing it well is the whole skill. More diluent means a
lower concentration, a larger draw volume, and a dose spread across more syringe marks — which reduces
measurement error. Less diluent means smaller draws and less refrigerator space. For microgram-level
doses, err toward more.
Bring everything to room temperature
Take the lyophilised vial and the bacteriostatic water out of cold storage and let them equilibrate.
Cold liquid injected into a cold vial dissolves more slowly and is more likely to be handled roughly to
compensate.
Inspect the powder cake. It should be intact and white to off-white. A collapsed, discoloured or
melted-looking cake indicates the vial has been through a temperature excursion.
Prepare a clean field and clean hands
Wash hands. Clear and wipe down a flat surface. Lay out: the peptide vial, the diluent vial, a
reconstitution syringe, alcohol pads, and a sharps container — before opening anything.
Remove the flip caps from both vials and swab both rubber stoppers with 70% isopropyl alcohol. Let
them air dry; alcohol needs contact time to work, and wiping it off immediately defeats the purpose.
The stopper is not sterile once the cap is off, and it stops being sterile again the moment it
is touched.
Draw the diluent
Draw the calculated volume of bacteriostatic water into the reconstitution syringe. Expel air
bubbles and verify the volume against the barrel markings at eye level — parallax at an angle is a real
source of error.
Bacteriostatic water contains 0.9% benzyl alcohol as a preservative and permits
repeated withdrawals over an extended period. Sterile water has no preservative and is
appropriate only where the vial will be used once, or where a compound is documented to be incompatible
with benzyl alcohol.
Add the diluent down the wall of the vial
Insert the needle through the stopper at a slight angle and direct the stream against the
inside wall of the vial so it runs down onto the powder rather than jetting into it. Tilting
the vial to roughly 45° makes this easier and reduces foaming.
Add the diluent slowly. Peptides are long chains held in a fragile three-dimensional shape, and the
shear force of a fast stream hitting the powder directly can break them.
Swirl — never shake
Roll the vial gently between the palms or swirl it in slow circles. Leave it to stand for a few
minutes if the powder has not fully dissolved; most peptides go into solution within a minute or two
without any agitation at all.
Shaking denatures peptides. It also creates foam, and foam at the air–liquid
interface is where denaturation happens fastest. If the solution foams, let it settle before drawing.
Inspect the solution
The solution should be clear and free of particulate. Exceptions worth knowing: GHK-Cu and any
blend containing it will be distinctly blue — that is the copper complex, and its absence is the red
flag rather than its presence.
Cloudiness, haze, visible fibrils or floating particulate indicate aggregation, degradation or
contamination. Amylin-family peptides such as cagrilintide are particularly aggregation-prone. A hazy
vial is not a cosmetic problem.
Label the vial immediately
Write on the vial: compound, vial strength, diluent volume, resulting concentration, and
the date of reconstitution. Do it now, not later.
An unlabelled vial in a fridge two months from now is unusable — not because the contents have
necessarily degraded, but because nothing can be calculated from it and nothing recorded about it means
anything. This is the single most common failure in self-directed work, and it is free to avoid.
Store correctly
Reconstituted: refrigerate at 2–8 °C, protected from light. Store toward the
back of a shelf, not in the door — the door cycles through the widest temperature swings.
Lyophilised (unreconstituted): −20 °C for long-term storage, refrigerated
for shorter periods, protected from light. Lyophilised peptide is dramatically more stable than
solution, which is why vials are supplied that way.
Avoid repeated freeze–thaw cycles of reconstituted solution. Each cycle is a stress event.
Understand the in-use window
General reference figures for peptide solutions are on the order of weeks at 2–8 °C and
months at −20 °C — but stability is compound-specific and the figures circulating in the
research community are largely unverified for the specific molecules on this site.
The practical issue is arithmetic: a 10 mg vial at a 1 mg weekly dose is ten weeks
in the refrigerator. That is well beyond the in-use period any approved peptide product would carry.
The calculator flags this when it happens.
