Packaging extractables and leachables

A vial and a stopper are not inert. They contain antioxidants, accelerators, plasticisers, lubricants and coatings, and some of those substances migrate into the product or its headspace. For a lyophilised peptide the amounts are usually small, but “small” is not “zero”, and the species involved can be reactive. The distinction between what a material can release and what it does release into your product is the whole subject.

Two words that are not interchangeable

Term	Definition	How it is studied
Extractables	Substances that can be extracted from a packaging component under aggressive laboratory conditions	Forced extraction with solvents, heat and time; analysis by GC-MS, LC-MS and ICP-MS
Leachables	Substances actually found in the product under real storage conditions	Analysis of the product or placebo at timepoints, with methods sensitive enough for the expected levels

An extractables study answers “what is in this material”. A leachables study answers “what reached my product”. A supplier who provides only the first has described the container, not the compatibility of the container with the peptide. The relevant framework is USP <1663> for extractables assessment and USP <1664> for leachables assessment, alongside the container standards such as USP <661> and the pharmacopoeial glass monographs.

Where the substances come from

Component	Typical sources	Why a peptide might care
Elastomer stopper	Vulcanising agents, accelerators, antioxidants, plasticisers, fillers, silicone oil	Reactive species can modify Lys or N-terminal groups; silicone can adsorb peptide and create particles
Glass vial	Alkali and boron oxides, forming lubricants, tungsten from the forming needle	pH shift during storage; delamination particles; tungsten residues in the base
Coatings and films	Polymer resins, adhesion promoters, solvents	Oligomers and residues can migrate; coating integrity is a variable
Labels and adhesives	Acrylic or rubber adhesives, inks, varnishes	Adhesive components can pass through a permeable secondary pack or contaminate the outer surface
Secondary packaging	Plastic bags, foils, desiccant sachets	Volatile organics in the headspace of a sealed pouch; desiccant dust

Silicone oil deserves separate mention. It is used as a lubricant on stoppers and syringes, it is not a single pure compound, and it can form visible droplets or a film on the inside of a vial. For a peptide, the concerns are particle formation and adsorption of hydrophobic sequences onto the silicone layer — a loss that is easy to miss because the solution remains clear.

Why lyophilised powder is not automatically safe

Direct contact between a dry cake and the stopper is limited, which reduces extraction compared with a liquid-filled vial. Three routes remain:

Vapour transfer. Volatile extractables enter the headspace and can partition into the cake, especially during long storage or temperature excursions.
Contact at the interface. The cake touches the vial wall and the stopper in places; a stopper that is pushed in after filling contacts the product directly.
Reconstitution. The solvent that dissolves the peptide also dissolves or disperses whatever is on the surfaces it touches, so a leachable that was immobile in the dry state can become mobile in solution.

The last point is the one most often overlooked: compatibility should be assessed for the reconstituted solution as well as the powder, because that is when the product is in contact with the container as a liquid.

How an assessment is structured

Define the contact material. Glass type, stopper formulation and coating, any silicone oil, secondary pack. “Pharmaceutical-grade vial” is not a specification.
Extract the components. Use solvents that bracket the product: aqueous at relevant pH, an organic solvent, and heat. Analyse the extract for volatile, semi-volatile and elemental species.
Build the extractables list. Identify what is present, at what level, and with what toxicological or reactivity concern.
Correlate to the product. Develop methods sensitive enough to detect the listed species in the product matrix, and run them on stored samples.
Assess the risk. Compare leachable levels with a safety or quality threshold, and consider reactivity with the peptide, not only toxicity.

This is product-specific work. A study performed on a different formulation, a different stopper lot or a different fill volume is supporting information, not a conclusion. That is why a supplier's container certificate can be genuine and still not answer your question.

What can go wrong with a peptide specifically

Adduct formation. Reactive carbonyls or aldehydes from a stopper can form Schiff bases with lysine side chains or the N-terminus, producing a mass shift that looks like a degradation product.
Oxidation. Peroxides and radicals from packaging components can oxidise Met, Trp or Cys, particularly in the presence of trace metals.
pH drift. Alkali leaching from glass raises the pH of a low-buffer solution, changing solubility and accelerating deamidation.
Particles. Silicone droplets, glass flakes and delamination are visible or sub-visible particles that a 0.22 µm filter is not designed to remove.
Adsorption. Peptide lost to a silicone film or a coated surface is a potency loss that no certificate will show.

What a supplier can document — and what it cannot

Document	What it supports	What it does not
Container specification (glass type, stopper formulation)	Identifies the materials of construction	That they are compatible with your peptide
Container compliance statement (USP <661>, Ph. Eur. 3.2.1)	The container meets a pharmacopoeial standard	That no leachables reach the product
Extractables study on the components	A candidate list of species and levels	That those species are present in the product
Leachables study on the product	What was found under the studied conditions	That nothing else is present below the method's limit
“Pharmaceutical grade” claim	Marketing language	Any of the above

For research-grade material, a full leachables package is uncommon and may not be proportionate. What is reasonable to ask is: which container and stopper are used, is the stopper coated or siliconised, has any extractables work been done on those components, and have customers reported particle or adduct issues with this product. The answers are more useful than a logo.

Practical checks on arrival

Inspect the vial and stopper for silicone droplets, discolouration, cracks and loose particles.
After reconstitution, view against a dark background for sub-visible haze and droplets; a hand-held light at a low angle helps.
If a mass shift appears in the intact MS, consider an adduct before assuming a degradation pathway.
For long storage, keep the vial upright and avoid repeated stopper penetration; each puncture creates a path and a particle source.
Record container and stopper lot numbers where the supplier provides them, so a packaging change can be traced.

Packaging is part of the specification, not an afterthought. The choices that reduce moisture and oxygen ingress are covered in packaging configurations; this article is about what the materials themselves can add to the product.

For laboratory research use only. This article describes packaging assessment concepts; it makes no claim that any container, stopper or product has been tested for extractables or leachables, and does not support administration to humans or animals.

Editor's take

Packaging is a reagent. Extractables from stoppers, coatings and labels can enter the product, and the risk rises with organic solvents and long contact times.

Limitations

This guide describes methods and interpretation, not acceptance limits. Limits must come from your own specification and, where applicable, the relevant pharmacopoeial monograph. No testing was performed by the author for this page.