Would you re-test dulaglutide after eight weeks at 37 °C, or accept the original certificate?

Stated plainly: dulaglutide · eight weeks · 37 °C.

I would like to set this up properly once, rather than adjust it repeatedly.

My budget is real but not tight, and my tolerance for uncertainty is low.

What should I decide now, and what should I defer?

eight weeks is 56 days, and at 37 °C the ten-degree rule of thumb makes that roughly 515 refrigerated days of equivalent exposure. 37 °C is 32 kelvin above the 5 °C middle of a 2–8 °C refrigerator. The ten-degree rule of thumb — degradation rate roughly doubling per 10 K — makes that about 9.2 times the refrigerated rate, which is an order-of-magnitude statement and not a shelf life. Compare that against what the certificate covers, which is the material as it left the laboratory on the date of analysis and nothing after it. 515 equivalent days is past the point where the original figure is evidence about the current vial, so the honest answer is that you no longer have a certificate for what you are holding. If you do re-test, send it for content as well as purity; the 56 days will have moved one of them further than the other.

The practical consequence is that spot-testing one vial from a new supplier is better than assuming they are all the same.

Under AQL sampling plans, testing two vials from a fifty-vial lot gives you an operating characteristic curve that tells you what risks you are accepting.

Reconciling gross mass to label claim

Specifically, if the entire lot failed qualification, a retest on a different vial is sometimes done, but reporting a retest result under the same lot number is misleading.

One qualification: testing more vials gives better confidence, but at some point the cost outweighs the benefit.

Assume segregation is possible, and design your sampling to catch it if it exists.

edited 13 Apr 2026 by esben_lykke — updated for the 2026 guidance change

The honest statement is that unless you have tested multiple vials or have segregation data, you are making an assumption about lot homogeneity that may not hold.

Acceptance Sampling by Attributes defines the number of samples you need from a lot to claim a specified quality level at a specified risk — it is in ANSI standard Z1.4.

On the detail: stratified sampling — testing one vial from the top, one from the middle, and one from the bottom of a shipment — is cheap insurance against segregation.

The practical summary: a lot number without a sampling statement is a lot number without meaning.

The relevant detail is that if a lot has visibly segregated — some vials showing different appearance — then sampling the top and bottom of the shipment is worth doing.

If you have reason to suspect inhomogeneity — different appearance in different vials, or a long or warm shipment — testing more vials is the diagnostic move.

For a quantitative result like content, the acceptable range determines how many vials you need to test to establish the lot complies.

Lyophilised peptide homogeneity studies show that vial-to-vial variation is usually small but occasionally large, depending on the distribution in the freeze-dryer.

If testing multiple vials, state how many you tested and why you chose those vials.

Put another way, batch testing establishes what can be claimed about the lot as a whole, and the sample size determines how much you can actually claim.

A statement that "lot 20260412 complies with specifications" is meaningless without stating which vials from the lot were tested and how many there were.

The caveat is that sampling is a trade-off between cost and confidence, and neither test nor assumption is cost-free.

If you only pay for one test, pay for quantified content. Purity is the number everyone quotes and content is the number that changes what you do.

The part that matters: the single most misleading statement on a research-grade certificate is a lot number with no statement of how many vials from that lot were tested.

Published segregation failures show that even modern automated processes sometimes produce lots with measurable vial-to-vial variation.

Sampling plans for pharmaceutical manufacturing are defined in ISO 2859 and ANSI Z1.4, and they are based on statistical sampling theory.

In practice: ask for the chromatogram, check the method section, check the lot number against the vial, and set your accept threshold before you see the result rather than after.