Storing Peptides

Why the powder keeps and the liquid does not

Peptides arrive as white powder because the water was pulled out of them. The maker froze the peptide, then put it under vacuum so the ice turned straight into vapour without melting first.

Take the water away and the molecules are stuck in place. Scientists call it a glassy state. Think of hard candy. Nothing inside can move, so nothing inside can react. That is why dry powder keeps for years.

Add water, heat, or light and you unlock it. That is when the clock starts.

The four things that destroy peptides

1. Moisture

The glassy state has a temperature at which it goes soft. Above that point the molecules can move again. Dry powder holds out until roughly 80°C, far above anything in your house.

Moisture drags that number down. Roughly:

• Almost no moisture: soft at about 80°C
• 3% moisture: about 50°C
• 8% moisture: about 25°C — ordinary room temperature

At that last point your powder has gone soft while sitting on a shelf, and it is breaking down. (Exact figures vary between products. The direction never does.)

2. Heat

As a rule of thumb, every 10°C warmer roughly doubles the speed of breakdown.

Start from a fridge at 4°C. Warm it to 14°C and breakdown runs at double speed. At 24°C, four times. At 34°C, eight times over. An afternoon on the counter costs more than it feels like it should.

3. Light

Light damages certain amino acids, and tryptophan is the most sensitive. There is a nasty twist: the damaged pieces are themselves light-sensitive, so damage speeds up damage. Tyrosine, methionine and cysteine are vulnerable too. Keep vials in the dark, in their box, away from windowsills.

4. Oxygen

Good manufacturers seal vials under vacuum or nitrogen, so there is no oxygen inside. The first needle through the stopper changes that, and every draw after lets a little more air in. A half-used vial sitting for months has had a lot of air.

The two clocks — the part almost everyone misses

Adding water starts two separate timers. They measure completely different things.

Those 28 days tell you about germs. They tell you nothing about whether the drug still works.

A vial can be free of germs and chemically dead. It can also be full of strength and full of bacteria. Two questions. Two different answers.

What benzyl alcohol does and does not do

It does hold bacteria back, and it numbs slightly, so injections can sting less.

It does not protect the peptide itself. It does nothing against chemical breakdown, and there is research showing it can actually destabilise some proteins and encourage them to clump.

So bacteriostatic water is not automatically the better choice. It is the right choice for a vial used over weeks. For a single day, plain sterile water is fine.

Never freeze it once mixed

Dry powder in a freezer is fine. Liquid in a freezer is not. Four things go wrong:

1. Ice crystals physically tear the peptide apart.
2. Freeze concentration. As ice forms, everything dissolved gets squeezed into the shrinking liquid, and the sudden crowding makes molecules clump.
3. Surface damage. Peptides stick to ice surfaces and unfold.
4. pH swings as different components freeze at different rates.

If you freeze one by accident: thaw it at room temperature, use it soon, never refreeze, and accept you have probably lost some of it.

What to look for, and what looking cannot tell you

A mixed vial should be clear, with nothing floating in it. Throw it out if you see:

• Cloudiness or haze — the molecules are clumping
• Visible bits floating — clumping far enough along to see
• Colour change, especially yellowing
• Anything gel-like
• An unusual smell

Which liquid to use

Bacteriostatic water

0.9% benzyl alcohol. Good for 28 days refrigerated after the first puncture. The default for a vial used over days or weeks.

Sterile water

Nothing added. Single use. Fine when the vial is finished in a day.

Sterile saline

0.9% salt, no preservative. Single use. Often more comfortable, and used where benzyl alcohol is a problem.

0.6% acetic acid

Only for peptides that specifically need it. Not a general option.

Storage table

Confidence is our reading of the evidence behind each row. High means manufacturer data or published research. Moderate means suppliers agree and there is a sensible basis. Low means sources conflict or it is an educated guess.

The honest part

Most of these compounds are sold as research chemicals. Their makers are not required to run the stability studies a pharmaceutical company must run.

So a lot of storage guidance — including some in the table above — is worked out from general chemistry, thin manufacturer data, or the USP microbial standard, rather than from testing that specific peptide.

What is genuinely solid:

• Cold slows every kind of breakdown. That is basic chemistry.
• Light damages certain amino acids.
• Freezing a mixed solution damages it.
• Without a preservative, bacteria grow.
• 28 days is a cautious microbial limit.

What this page cannot tell you: how potent your vial is today, whether your particular vial is still good, or what your own handling has cost it.

When you are not sure

• Sources disagree? Take the shorter figure.
• No data at all? Treat it as good for two to three weeks once mixed.
• A blend? Assume the stability of its weakest ingredient.
• Unsure about bacteriostatic water? Use sterile water for a single dose.
• Left somewhere warm or bright? Use it sooner, or bin it.
• Looks wrong? Bin it. A replacement vial costs less than an infection.

Think we got something wrong? Here is how we fix mistakes.