Vial (revision 47)

A vial is a small container, conventionally of glass, closed by an elastomeric stopper retained under a crimped metal ferrule. It is the standard primary package for injectable products and for lyophilised solids, including the great majority of peptides distributed for research use. The vial, its closure and its seal are treated in pharmaceutical practice as a single functional unit — the container closure system — because none of the three performs its function without the others.^[1]

The container has three simultaneous duties. It must contain the product without contributing to it, which constrains the chemistry of both glass and elastomer; it must exclude micro-organisms and, for many products, moisture and oxygen, which is a matter of seal integrity rather than of material; and it must permit withdrawal by needle without loss of that integrity, which is why the closure is a penetrable elastomer rather than a screw cap.^[2][1]

Failures of each duty are documented and distinct. Leaching of glass constituents alters solution pH and can catalyse degradation; inner-surface delamination sheds glass flakes and was the subject of regulatory advisories and recalls in 2010 and 2011; incomplete sealing permits microbial ingress and moisture gain, the latter raising the residual moisture of a lyophilised cake over its shelf life; and coring of the stopper by a needle introduces elastomer particles into the withdrawn liquid.^[3][4][5]

For material distributed outside pharmaceutical channels, the vial is also the principal carrier of identity. A label, a crimp colour and a stamped lot number are frequently the only evidence linking a solid to a certificate of analysis, and the ease with which all three can be reproduced is the structural reason that lot traceability in that sector is weak.^[1]

Pharmaceutical glass vials are produced by two routes with different characteristics.

Tubing-drawn vials are formed by softening a length of drawn borosilicate tubing and shaping the base and neck. Wall thickness is set by the tubing and is thin and uniform; dimensional tolerances are close; and the process is fast, which makes tubing the route for small vials produced in quantity. Because the neck and base are formed by localised heating, the inner surface at those points reaches higher temperatures than elsewhere and is chemically altered, which is the origin of the delamination susceptibility discussed below.^[4]

Moulded vials are formed by pressing molten glass in a mould. Walls are thicker and less uniform, tolerances looser, and the vials heavier and more robust. Moulding dominates for larger containers and where mechanical strength matters more than dimensional precision.^[6]

Polymer vials of cyclic olefin polymer or copolymer are established for products incompatible with glass or requiring extreme resistance to breakage. They eliminate delamination and alkali leaching, and they permit lower moisture-vapour barrier performance and different extractable profiles — trade-offs rather than improvements. Requirements for plastic packaging systems are set out in USP <661> and its subsidiary chapters.^[7]

The classification is by measured hydrolytic resistance rather than by nominal composition, and the tests differ between types: powdered glass tests interrogate the bulk composition, whereas the water attack test interrogates the treated inner surface. The European Pharmacopoeia operates a closely comparable scheme through general chapter 3.2.1 and the ISO 719 and ISO 720 grain tests.^[8][9]

Type I borosilicate is specified for essentially all injectable products. Its low alkali content limits pH shift on storage, and its linear expansion coefficient of roughly 32–33 × 10⁻⁷ K⁻¹ — about a third that of soda-lime glass — gives the thermal shock resistance required for depyrogenation at 250 °C or above and for the thermal cycling of a lyophilisation cycle.^[8]

Glass vials are rendered free of endotoxin by dry heat, conventionally at 250 °C or above for a validated period, with the requirement expressed as a demonstrated reduction of at least three logarithms in a challenge of bacterial endotoxin rather than as a time and temperature alone. The process is destructive to endotoxin rather than merely sterilising, which is why it is specified separately from sterilisation and why autoclaving does not substitute for it. Verification of the result is by the bacterial endotoxin test described in USP <85>.^[8][1]

Vial sizes are standardised by ISO 8362-1 in a series designated by a number and the letter R, the number being the nominal capacity in millilitres. The nominal capacity is not the volume the vial holds: the brimful or overflow capacity is substantially larger, because headspace is required for stoppering, for the expansion of a lyophilisation cake and for withdrawal.

Dimensions are nominal and subject to the tolerances in the standard.^[6] Two consequences follow for reading a label. A vial described as a 2 mL vial holds about 4 mL brimful, so a 2R vial containing 1 mL of liquid looks nearly empty and a 2R vial containing a 5 mg lyophilised cake may appear to contain nothing at all. And the neck finish, not the nominal capacity, determines which closure fits — 13 mm and 20 mm are not interchangeable, and a 20 mm stopper on a 13 mm vial cannot be sealed.

The label declaration for an injectable is the volume or mass withdrawable, and vials are therefore filled with a small excess. USP <697> requires that the volume obtainable be not less than the labelled volume, and USP <1151> gives recommended excess volumes for that purpose.

Figures are those recommended in the general chapter for single-dose containers.^[10][11] A worked case shows how thin the margin is in practice. A vial labelled 2.0 mL and filled to 2.15 mL is withdrawn with a syringe of 0.07 mL dead space; the withdrawable volume is reduced by the dead space and by whatever the vial geometry traps at the base, so the nominal 0.15 mL excess is very largely consumed by the device. For a reconstituted research peptide, where the operator chooses the diluent volume, the same arithmetic governs how much of the nominal fill is actually obtainable, and it is the reason a nominal ten-dose vial commonly yields fewer.^[10]

The stopper performs three functions: it seals, it is penetrable by a needle and reseals afterwards, and it must not contribute leachables to the product. No single elastomer optimises all three, and formulation is a compromise.

Butyl elastomers dominate because their low permeability protects a lyophilised cake from moisture ingress and an oxygen-sensitive product from oxidation over a multi-year shelf life. A closure formulation is a mixture of elastomer, filler, curing system, pigment and lubricant, and the components other than the elastomer are frequently the source of the extractables that make a closure unsuitable for a particular product.^[2][12]

Fluoropolymer lamination — a thin film of a fluorinated polymer applied to the product-contact face — is the standard mitigation. It reduces extractables and adsorptive loss of peptide onto the stopper surface without altering the bulk mechanical properties on which sealing and resealing depend. Silicone-oil lubrication of the outer surface aids machine handling but is itself an extractable and a source of subvisible particles.^[12]

Closures for freeze-drying are a distinct type, specified in ISO 8362-5. Their skirt geometry permits the stopper to be seated partially, resting on lugs so that vapour can escape during drying, and then pressed fully home by the dryer shelves at the end of the cycle while the chamber is still evacuated or backfilled with nitrogen. The headspace composition of a lyophilised vial is therefore determined by the freeze-dryer, not by the filling room.^[5]

USP <381> sets the compendial requirements for elastomeric closures, including biological reactivity, physicochemical tests on aqueous extracts, self-sealing and fragmentation. The self-sealing test requires that a defined number of penetrations produce no leakage; the fragmentation test limits the number of visible elastomer fragments released into a liquid across a specified number of penetrations. The European Pharmacopoeia general chapter 3.2.9 imposes closely comparable tests.^[2][13]

Coring is the excision of a plug or fragment of elastomer by a needle passing through the closure. It occurs when the needle cuts rather than parts the elastomer, and its likelihood rises with needle diameter, with a blunt or damaged bevel, with penetration perpendicular to the surface rather than at an angle, and with repeated penetration through the same point.^[2]

The consequences are two. A fragment may be drawn into the syringe and injected, which is a particulate-contamination event; and the resulting channel may compromise the seal of a container intended for further withdrawals, which is a integrity event and matters chiefly for multiple-dose containers.

Compendial fragmentation testing quantifies the propensity: a specified number of penetrations is made with a needle of specified gauge through closures on filled vials, the contents are filtered, and the visible fragments counted against a limit. Because the test is performed with a defined needle and technique, it characterises the closure rather than any particular pattern of use, and a closure that passes can still be cored by a blunt needle used repeatedly at one point.^[2][13]

The stopper is retained by an aluminium ferrule crimped beneath the vial's neck flange. The crimp compresses the stopper flange against the sealing land of the vial, and it is that compression — not the stopper alone and not the ferrule alone — that produces the seal.

The mechanical figure of merit is residual seal force: the compressive force remaining on the stopper after crimping and after the elastomer has relaxed. Too little leaves an unreliable seal; too much can distort the stopper, damage the glass sealing surface or crack the flange. Residual seal force is measurable non-destructively and has become the conventional in-process control for capping, replacing subjective assessments such as attempting to rotate the cap by hand.^[14][1]

Ferrule designs differ in how the closure is later opened. A plain ferrule fully covers the stopper and must be removed with a decapping tool. A flip-off design carries a plastic button over a pre-cut aperture, which is lifted away to expose the central area of the stopper for needle penetration while leaving the crimp intact — the arrangement almost universal for injectable products and for research peptide vials. Colour of the button is a manufacturer's identification device with no standardised meaning, and it is not a reliable indicator of contents.^[5]

Two consequences bear on handling. Once a flip-off button is removed, the exposed stopper surface is no longer protected, and its disinfection before each penetration is the compendially expected practice for multiple-dose containers. And the crimp is not intended to be removed and replaced; a vial whose ferrule shows evidence of having been decapped and recrimped has an unknown seal history, which is a recognised indicator in the examination of suspected repackaged or counterfeit material.^[1]

Integrity is the ability of the container closure system to prevent ingress of micro-organisms and, where required, to maintain headspace composition. USP <1207> is the governing informational chapter and it reorganised thinking on the subject by classifying methods as deterministic or probabilistic.^[1]

Deterministic methods measure a physical quantity related to leakage, give quantitative results, and are reproducible: helium mass-spectrometric leak detection, vacuum decay, pressure decay, laser-based headspace analysis, and high-voltage leak detection. Probabilistic methods depend on a chain of stochastic events and give a pass or fail: microbial immersion challenge, dye ingress, and bubble tests. The chapter's position is that deterministic methods are preferred wherever available, and that probabilistic methods are appropriate mainly as qualitative confirmation.^[1][14]

The chapter also frames integrity in terms of a maximum allowable leakage limit — the largest leak that can be tolerated without compromising the product — which is to be established for the specific product rather than assumed. For microbial ingress, the leak size below which passage becomes improbable has been studied experimentally, and the frequently cited threshold of the order of a few micrometres derives from that work rather than from a compendial requirement.^[1][14]

• Multi-dose vial
• Vial filling and stoppering
• Lyophilisation
• Beyond-use date
• Reconstitution of lyophilised peptides
• Underfilling
• Repackaging

• Sacha GA, Saffell-Clemmer W, Abram K, Akers MJ. "Practical fundamentals of glass, rubber, and plastic sterile packaging systems." Pharmaceutical Development and Technology 15(1):6–34 (2010).
• Guazzo DM. "Container closure integrity testing" in Sterile Product Development, Springer (2013).