Retest date vs expiry date on a peptide label: what each date claims

Three dates that are often confused

A peptide container and its paperwork can carry a manufacture date, a certificate or analysis date, and either a retest date or an expiry date. Buyers ask whether a "retest" date means the material expires then, and whether an older certificate makes the lot stale. The vocabulary comes from good manufacturing practice guidance for active pharmaceutical ingredients, which gives precise definitions.

Research-grade suppliers may not operate under that guidance. Use its definitions as a common language for questions, not as evidence that a supplier follows it. This guide gives no stability or storage limits of its own.

The ICH Q7 definitions

ICH Q7, the GMP guide for active pharmaceutical ingredients, defines an expiry (or expiration) date as "the date placed on the container/labels of an API designating the time during which the API is expected to remain within established shelf life specifications if stored under defined conditions, and after which it should not be used." It defines a retest date as "the date when a material should be re-examined to ensure that it is still suitable for use." [1]

Section 11.6 adds that an API expiry or retest date should be based on an evaluation of data derived from stability studies, that common practice is to use a retest date rather than an expiration date, and that a representative sample should be taken for the purpose of performing a retest. [1] FDA publishes ICH Q7 as a final guidance for industry, dated September 2016. [2]

Read the storage condition with the date

An expiry date is defined in relation to defined storage conditions. [1] A date copied without its condition is incomplete. Record the stated condition exactly as written on the label or certificate, and note whether the date refers to an unopened container. If the paperwork is silent, ask the supplier rather than borrowing a condition from another product.

If your shipment had a temperature concern, keep that record separate and let your qualified reviewer decide whether the stated date still applies. The shipping excursion guide on this site describes that record.

A fictional mismatch

An invented certificate shows an analysis date two years before receipt and a retest date that has already passed; the vial label shows no date. The defensible note is: "Retest date on certificate has passed; no later retest record supplied; label carries no date." The next action is a written request for any retest certificate for this lot, with its method and date.

Do not write that the material has degraded; nothing in the record shows that. Do not extend the date yourself. A retest is a test, and its result belongs in a dated certificate tied to the lot.

What to keep on file

Keep the original label photograph, the certificate, any retest certificate, the supplier's stated storage condition and your receiving date. When a supplier issues a new retest result, append it rather than replacing the earlier record, so the history of the lot remains visible.