Would you re-test semaglutide after twelve weeks at 2–8 °C, or accept the original certificate?

Concretely: semaglutide · twelve weeks · 2–8 °C.

I want to decide this in advance so that I am not deciding it under pressure later.

Assume I will follow the plan I write down, so I would like it to be a good one.

How would you structure this, and what thresholds would you set in advance?

twelve weeks is 84 days, and at 2–8 °C the ten-degree rule of thumb makes that roughly 84 refrigerated days of equivalent exposure. 2–8 °C is the condition the rule of thumb is anchored to, so it is the baseline rather than a multiplier: everything else in this thread is quoted relative to it. 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. That is short enough that a re-test is a stability study rather than a safety check — worth doing if you will publish the result, hard to justify if you will only reassure yourself. If you do re-test, send it for content as well as purity; the 84 days will have moved one of them further than the other.

Stated carefully, sampling plans exist precisely because testing everything is expensive, and they define the statistical relationship between sample size and lot-wide inference.

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

Reconciling gross mass to label claim

If the lot was manufactured in multiple batches, testing vials from each batch separately establishes whether batch-to-batch variation is acceptable.

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 31 Aug 2024 by eighty_six_hours — added a caveat about sampling

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.

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

The relevant detail is that testing a vial that has been open in the lab for three months is testing aged material, not the fresh lot, and the result should be explicitly noted as a retest.

Worth noting that thermal excursions during shipping affect different vials differently, so the lot may not be homogeneous even if it left the factory that way.

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

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

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.

It helps to be literal here: 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.

Published data on lot homogeneity from manufacturers who sample multiple vials consistently find variation below the published specifications, suggesting the sampling plans work.

The limitation is that you cannot know for certain without testing every vial, and you almost never can afford to do that.

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