How do I write up a PeptideMeter result on liraglutide so it is useful to others?

Setup, so nobody has to ask: PeptideMeter · liraglutide.

I have done this once and I suspect I got away with it rather than got it right.

For context: I keep records of every batch, every lot number and every result, so an answer that requires me to track something is fine.

What would you do, and what would you check afterwards?

On the detail: 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.

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

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

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.

Put another way, 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.

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

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.

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

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

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

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

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

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

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

edited 19 Jul 2024 by ravenna_pace — expanded the table to cover the lower concentration

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.

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 ICH Q3A and Q3B thresholds for reporting, identification and qualification of impurities are the framework the pharmaceutical industry works to, and they are worth reading even though nothing in the research-grade supply chain is obliged to meet them, because they tell you which numbers a competent analyst would consider worth reporting at all.

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

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 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.

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.

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

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.