Lyophilized Peptide: Lyophilization and Storage

What is a lyophilized peptide?

A lyophilized peptide is a peptide that has been frozen and then dried under a vacuum until only a dry solid is left.

Lyophilized simply means freeze-dried. In a sealed vial, the dried peptide often looks like a small white cake or powder. Only the water is gone; the molecule is the same.

A sterile liquid called a diluent turns it back into a solution, a step called reconstitution. Our reconstitution guide shows how, the reconstitution calculator does the math, and the bacteriostatic water page explains why a dry vial needs one.

This page expands the short entry for lyophilized in our peptide glossary.

Sources: FDA, Guide to Inspections of Lyophilization of Parenterals; US label for bivalirudin, DailyMed; US label for human secretin, DailyMed.

How does lyophilization work?

Lyophilization works in three steps: freeze, turn the ice to vapor under a vacuum, then dry off the last water.

1. Freezing. Vials of peptide solution sit on chilled shelves, often near -40 °C, until most of the water is ice.
2. Primary drying. A pump pulls the air out of the chamber and the shelves warm a little. The ice turns straight into vapor without melting, a jump called sublimation.
3. Secondary drying. The shelves warm a bit more, still under vacuum, to pull off most of the water that never froze. This is called desorption.

The stoppers are usually pushed in while the vials are still inside the freeze-dryer. What is left is a porous cake, its tiny holes marking where the ice crystals were. The FDA notes that the water comes out without much heat, and that the dry cake dissolves quickly.

Sources: FDA, Guide to Inspections of Lyophilization of Parenterals; Patel and Pikal, AAPS PharmSciTech 2011, PMID 21347620.

Why do peptides ship as a dry powder?

Peptides ship dry because many are not stable in water, and taking the water out slows the chemical changes that break them down.

In water, a peptide can react with oxygen (oxidation), be split by water (hydrolysis), have a building block changed (deamidation), or clump together (aggregation). Each change leaves less of the original peptide.

That is why peptide and protein drugs are often made as solids for storage. The FDA lists better stability in the dry state as one benefit of freeze-drying. A 2025 review by FDA scientists calls the method a workhorse for storing unstable products and shipping them far.

Dry is not frozen in time, though. Chemical changes still happen in a dry solid, and heat and moisture speed them up.

Freeze-drying is also slow and costly, and one review notes that freeze-dried products, with their mixing liquid, can take up to twice the space of liquid ones. The point is stability, not cheaper shipping.

Sources: Nugrahadi et al., Pharmaceutics 2023, PMID 36986796; FDA, Guide to Inspections of Lyophilization of Parenterals; Lai and Topp, Journal of Pharmaceutical Sciences 1999, PMID 10229638; Rhieu et al., AAPS Open 2025, PMID 41743609.

How do you store a lyophilized peptide?

Keep a lyophilized peptide sealed, dry, cold and out of light. The dry vial keeps longer than the same peptide after mixing.

• Sealed and dry. Moisture speeds up breakdown even in a powder, so keep the vial closed until the day it is mixed.
• Cold for long storage. Lab guidelines say peptides kept longer than about six months do best freeze-dried at -20 to -80 °C.
• Dark. Some amino acids, such as tryptophan and phenylalanine, can break down in light.

The best temperature still depends on the peptide, as the US labels of three freeze-dried peptide medicines show:

These are prescription medicines, shown here only for their storage rules.

After mixing, the peptide is back in water and breaks down faster. Our reconstitution guide covers storing a mixed vial.

How long it lasts has no single answer: FDA inspectors expect each expiry date to rest on stability data for that one product.

Sources: Lai and Topp, Journal of Pharmaceutical Sciences 1999, PMID 10229638; Hoofnagle et al., Clinical Chemistry 2016, PMID 26719571; US label for bivalirudin, DailyMed; US label for corticorelin, DailyMed; US label for human secretin, DailyMed; FDA, Guide to Inspections of Lyophilization of Parenterals.

What is in the dry cake, and what does it not prove?

A cake holds more than the peptide, and freeze-drying alone proves nothing about purity or identity.

• A salt partner. Lab-made peptides often leave purification as salts, paired with a counter-ion such as trifluoroacetate (TFA) or acetate.
• A little water. Some moisture stays, and the FDA lists moisture testing among the checks for freeze-dried products.
• Other ingredients in some products, such as mannitol.

One US label shows how this adds up. Bivalirudin, a peptide medicine, comes as a white freeze-dried cake. Its label lists the peptide, its salt form and a bulking sugar, mannitol, as separate amounts, so the powder weighs more than the peptide in it.

Labs therefore report two separate numbers. Net peptide content is the actual peptide in a weighed sample, without the water and counter-ions. Purity is how much of the material is the right peptide rather than related impurities.

Freeze-drying is a drying step, not a cleaning step: it removes water, not look-alike peptides. Chains missing an amino acid, made by mistake during synthesis, and breakdown products can stay in a finished product. Purification removes by-products, and lab tests show purity (usually by HPLC) and identity (usually by mass spectrometry), as our guide to reading a certificate of analysis explains.

Sources: Sikora et al., Pharmaceuticals 2020, PMID 33287352; FDA, Guide to Inspections of Lyophilization of Parenterals; US label for bivalirudin, DailyMed; Hoofnagle et al., Clinical Chemistry 2016, PMID 26719571; D'Hondt et al., Journal of Pharmaceutical and Biomedical Analysis 2014, PMID 25044089.

What does a real certificate show for a freeze-dried vial?

A certificate turns these ideas into numbers you can check: amount, purity, identity and batch.

Here is our published certificate for one lot of Selank, a 10 mg freeze-dried vial, read from our certificate records:

1. Amount. The vial is sold as 10 mg, and the lab measured 10.19 mg of the peptide itself. That is 0.19 mg, or 1.9 percent, more than the label states. Net content counts only the peptide, not the water or salt.
2. Purity. Of everything the HPLC test detected, 99.10 percent was Selank and 0.90 percent was related substances. Amount and purity are separate results, so a certificate needs both.
3. Identity. Its HPLC retention time matched the time expected for Selank, and LC-MS confirmed its mass. The look of a cake cannot tell you that.
4. Batch. Lot SEL-260406-A ties these results to one batch, tested in June 2026.

To check it, open the Selank card on our certificates page or the full certificate as a PDF.

Our published certificates show measured purity between 95.48 and 99.62 percent. Each certificate names the independent third-party lab that issued it.

Data: our published certificate COA-2026-4806 and our certificate records. Sources: Hoofnagle et al., Clinical Chemistry 2016, PMID 26719571.