Why did two FGP lots of cagrilintide differ on content assay?

Stated plainly: FGP · cagrilintide.

This is not behaving the way I expected and I want to understand the discrepancy before I act on it.

I have photographed the current state and recorded the conditions, so I can answer follow-up questions precisely.

Is this recoverable, and how would I tell?

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.

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

Mass shifts and what they usually mean

Specifically, 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 29 Jul 2025 by b_delacroix — updated for the 2026 guidance change

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.

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.

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

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

A certificate that reports one test result on one vial extrapolates to claim that all two hundred vials in the lot are identical, which is an assumption worth questioning.

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.

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

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.

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

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.

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

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

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

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