Vial (revision 20)

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a lyophilised cake over its shelf life; and coring of the stopper by a needle introduces elastomer particles into the withdrawn liquid.^[3][4][5]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.

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][10]