Does a large published testing history at SWB imply lot consistency?

This is my second independent submission on material from the same supplier.

I suspect the usual explanation for this is wrong, or at least incomplete.

I am aware this may have a boring answer. I would still like the boring answer stated clearly.

Can someone derive this rather than assert it?

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.

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.

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.

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

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

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.

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

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.

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 part that matters: if the lot was manufactured in multiple batches, testing vials from each batch separately establishes whether batch-to-batch variation is acceptable.

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.

The part that matters: 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.

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.

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

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.

Start from the question: how many vials from this lot do I need to test to claim that the lot meets specification, and the answer depends on both the lot size and the acceptable risk.

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.

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

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.

edited 14 Oct 2024 by day_seven_trough — added the method parameters