Beyond-use date (revision 35)

A beyond-use date (BUD) is the date, or date and time, after which a compounded preparation or an opened container is not to be used. It is assigned by the person who prepares or opens the preparation, using compendial default tables or, where available, testing specific to the preparation. It is distinct from an expiration date, which is assigned by a manufacturer on the basis of a formal stability programme conducted on the finished product in its final container.^[1][2]

The distinction is one of evidence rather than of vocabulary. An expiration date rests on long-term, intermediate and accelerated stability studies conducted under the conditions specified in ICH Q1A(R2), analysed statistically, and submitted to a regulator; it is a claim about the specific product in the specific container. A beyond-use date generally rests on a table of conservative defaults chosen to be safe across a wide range of preparations, and it is a claim about a class of preparations rather than about the one in hand. The two are therefore not comparable quantities, and a short beyond-use date does not imply a preparation degrades quickly.^[3][1]

Beyond-use dates in sterile compounding are limited principally by microbiological risk rather than by chemical degradation. The default periods in USP <797> are graduated by how the preparation was made, by whether sterility testing was performed and passed, and by storage temperature — not by the chemistry of the active substance. Chemical stability is a separate constraint, and where it is shorter it governs.^[1]

The distinction between the two kinds of date is imperfectly maintained in secondary sources and in ordinary usage, where both are called an expiry. On this wiki the conflation has been the subject of a request for comment, and the resulting convention is that expiration date is reserved for manufacturer dating supported by a stability programme, and beyond-use date for everything else.^[4]

An expiration date is the output of a defined regulatory process. Under ICH Q1A(R2), a manufacturer conducts long-term studies at the intended storage condition, intermediate studies where required, and accelerated studies at elevated temperature and humidity, on at least three primary batches in the container closure system intended for marketing. The results are evaluated — under ICH Q1E — to establish a retest period or shelf life, and the date is stated on the label. It applies to the unopened product stored as labelled.^[3]

A beyond-use date has none of that apparatus behind it. It applies to a preparation that the manufacturer's stability programme never examined: a container that has been opened, a solution that has been diluted, a lyophilised solid that has been reconstituted, or a preparation compounded from components. The chemistry may be identical; the container's history is not.

Two consequences of the table are worth drawing out. Because the two dates are limited by different things, they respond differently to storage: refrigeration extends a microbiologically limited beyond-use date substantially and generally extends an expiration date not at all, since the expiration date already assumes the labelled condition. And because a beyond-use date is assigned rather than measured, it can be assigned correctly to a preparation that has in fact already degraded, if the degradation route was one the default table does not contemplate.^[1][2]

Where both dates apply, the earlier governs. A preparation compounded on a date that would yield a 45-day beyond-use date, from a component whose own expiration date falls in 20 days, has a usable life of 20 days.^[5]

USP <797> classifies compounded sterile preparations into categories by the conditions under which they are made, and assigns default beyond-use dates by category, by whether sterility testing was performed, and by storage temperature.

Category 1 preparations are made in an unclassified segregated compounding area and carry the shortest dating. Category 2 preparations are made in a cleanroom suite meeting the chapter's requirements. Category 3 preparations meet additional requirements — including sterility and endotoxin testing and more extensive personnel qualification — and may carry substantially longer dating.

Periods are those tabulated in the 2023 revision of the chapter, which differs from earlier revisions; the earlier low-, medium- and high-risk classification has been replaced by the category scheme.^[1]

Three structural features of the table repay attention. Sterility testing buys a large extension — from 4 days to 30 at room temperature for an aseptically processed preparation from sterile components — which reflects that the untested default is a bound on the probability of undetected contamination rather than an estimate of when contamination occurs. Introducing a nonsterile starting component shortens the dating sharply, because the bioburden and endotoxin history of that component is unknown. And frozen storage flattens the differences, because microbial growth is suppressed and the residual limit becomes chemical.^[1]

The chapter states throughout that the defaults are maxima and that a shorter date must be assigned where the chemical or physical stability of the preparation, or the compatibility of its components, requires it. The defaults bound microbiological risk; they say nothing about whether a peptide in the preparation remains intact.^[1][2]

Nonsterile compounded preparations are dated under USP <795>, which in its 2023 revision assigns defaults by dosage form and water activity rather than by a calculation from component expiry.

Periods are those in the 2023 revision.^[5] The revision removed a widely known earlier provision under which a preparation made from a manufactured product could be assigned a beyond-use date of not later than 25% of the time remaining until that product's expiration date, or six months, whichever was earlier. That 25% rule remains in circulation in secondary sources and in older references, and is no longer the compendial position; sources quoting it should be checked against the current revision.^[5][6]

The 2023 chapter also permits longer dating where supported by a stability-indicating study on the preparation, or by published stability information for the same formulation in the same container and storage condition. The qualification about container and condition is not incidental: published stability data for a solution in a glass vial does not transfer to the same solution in a plastic syringe, because sorption and permeation differ.^[5][6]

Water activity is the organising principle behind the dosage-form distinctions. Preparations in which water is available support microbial growth and hydrolytic degradation; those in which it is not, or is bound, support neither to the same degree. This is the same principle that makes a lyophilised solid far more stable than its reconstituted solution, and it connects the compendial framework to the physical chemistry set out at Lyophilisation.^[5]

Entering a container ends the applicability of its expiration date, because the container closure system on which that date depended has been breached. Dating from that point follows the rules described at multiple-dose containers and summarised here.

Single-dose containers

Entered in ISO Class 5 air or better, usable for up to 12 hours; entered in poorer air, up to 1 hour. The dependence on air quality reflects that the risk is airborne and personnel-borne contamination at the moment of entry.

Multiple-dose containers

28 days after initial puncture, unless the manufacturer specifies a shorter period. The preservative, not the environment, is what permits the longer period.

Pharmacy bulk packages

As stated on the label, conventionally a small number of hours after entry.^[1][7]

The 28-day figure derives from the antimicrobial effectiveness testing in USP <51>, whose challenge protocol runs over 28 days, together with infection-control practice. It is not a chemical stability figure and was never derived as one, a point on which this wiki has had to correct several articles.^[8][4]

• Multi-dose vial
• Vial
• Bacteriostatic water
• Reconstitution of lyophilised peptides
• Temperature excursion
• Cold chain