Would you re-test ecnoglutide after twelve weeks at 25 °C, or accept the original certificate?

The case in front of me: ecnoglutide · twelve weeks · 25 °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?

Thermal history during shipping is different for every vial, so a lot that experienced thermal abuse may have internal variation even if it was originally homogeneous.

The sample size determination requires choosing a confidence level and an acceptable error rate, and the smaller the error rate you want, the larger your sample must be.

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.

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

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

Most suppliers test one vial per lot and report the result as lot homogeneity, which is sampling one item from one lot and extrapolating wildly.

The statistical foundation here is well-established, which is why sampling plans from decades ago are still valid.

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

I would treat a "complies with" statement without sampling details as a claim rather than as evidence.

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

Specifically, the failure mode here is publishing a result that applies to the tested vial alone while implying it applies to the entire lot.

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.

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

edited 11 May 2024 by stopper_core — clarified the distinction between purity and content

Stated carefully, two vials tested from a lot of ten is very different from two vials tested from a lot of ten thousand, and most certificates do not state the lot size.

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.

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

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

edited 26 Jul 2024 by Dr_Ilse_Vandenberg — added a caveat about sampling