What the four services actually offer, test by test

Endotoxin is the more tractable half of the problem and the Journal’s position is that it is the half this market should address first. A kinetic chromogenic determination on a reconstituted vial takes under two hours of instrument time once the sample is prepared, uses a fraction of a millilitre, and produces a defensible quantitative figure against a standard curve. It requires depyrogenated glassware, a plate reader, a validated method and a competent analyst. It does not require a fortnight or a cleanroom.

The compendial sterility test, described plainly

The compendial test proceeds by one of two routes. In membrane filtration, the entire contents of the sampled containers are passed through a retentive membrane which is then divided between two growth media. In direct inoculation, the contents are transferred into the media directly. The media are a fluid thioglycollate medium incubated at thirty to thirty-five degrees for anaerobes and aerobes, and a soybean-casein digest medium incubated at twenty to twenty-five degrees for fungi and aerobes. Incubation runs for fourteen days with periodic examination for visible growth.

The number of containers sampled depends on batch size, and for a parenteral batch above five hundred containers the requirement is twenty. Every one of those twenty is destroyed. Method suitability must be demonstrated separately, because a preserved formulation or an antimicrobial residue can inhibit the very growth the test is looking for, and the bacteriostatic and fungistatic properties of the article have to be neutralised or shown absent before a negative result means anything.¹

A reader who takes nothing else from this section should take the sample size. Twenty containers, fourteen days, destroyed. That is the entire empirical basis of the finished-product sterility claim, and it is why the process argument carries the weight.

Low endotoxin recovery, and the clean result that is wrong

The most uncomfortable finding in endotoxin testing over the past fifteen years is that certain formulation matrices cause added endotoxin to become undetectable over time. Spike a known quantity of reference endotoxin into a solution containing a non-ionic surfactant and a chelating buffer, hold it, and the recoverable endotoxin declines — sometimes to a small fraction of what was added — while nothing has been removed. The lipopolysaccharide aggregate state has changed, and the assay cannot see what it cannot bind.

The phenomenon is called low endotoxin recovery, and it matters because the combination of polysorbate with citrate or phosphate is extremely common in peptide and protein formulations. A hold-time study — spiking the actual product matrix and measuring recovery across the intended sample storage interval — is the standard mitigation, and it is now expected as part of method suitability for products in that formulation space.

The implication for a reader is narrow but worth stating. A negative endotoxin result on a surfactant-containing formulation, reported without a hold-time recovery study, is weaker evidence than it appears. A negative result on a reconstituted lyophilised peptide in plain water for injection, tested promptly, is considerably stronger.²

Container closure integrity, method by method

The compendial guidance divides leak test methods into probabilistic and deterministic families and is explicit about preferring the second. Probabilistic methods — dye ingress under vacuum, microbial immersion challenge, bubble emission — rely on a sequence of stochastic events, and their sensitivity is poor and hard to quantify. A dye ingress test can pass a container with a defect large enough to admit an organism, because the dye happened not to travel.

Deterministic methods measure a physical quantity with a continuous response. Vacuum decay monitors pressure rise in an evacuated test chamber. High-voltage leak detection measures current through the container wall and is well suited to liquid-filled units. Laser-based headspace analysis interrogates the gas inside a sealed container non-destructively, which permits repeated measurement of the same unit across a stability programme. Helium mass spectrometry resolves the smallest defects of any method in routine use.

The threshold that matters is the maximum allowable leakage limit — the defect size below which microbial ingress does not occur under the conditions the product will see. Establishing it for a given package is a piece of work, and once established it converts an argument about seals into a measurement.³

What the cake tells you

A lyophilised plug is a physical record of the cycle that produced it. A well-formed cake occupies close to the volume of the solution that was frozen, has a matte, uniform appearance, retains a defined edge where it met the glass, and dissolves rapidly and completely on addition of diluent. That appearance indicates that the product was frozen below its critical formulation temperature and dried without the structure collapsing.

Departures are informative. A shrunken, translucent or glassy plug suggests collapse during primary drying — the ice sublimed faster than the amorphous matrix could hold its structure — which is associated with higher residual moisture and a shorter shelf life. A cake that has partly detached and moves freely suggests mechanical handling after drying, which is cosmetic. A cake showing melt-back at the base, or a visible meniscus line, suggests a shelf temperature excursion. Slow or incomplete reconstitution suggests either collapse or an unfavourable surface.

None of these observations is a purity finding, a sterility finding or an endotoxin finding, and it is important not to overclaim. What they are is the only direct evidence about process control that arrives in the box, and reading them costs nothing. The Journal photographs every cake it receives before opening the vial, for exactly that reason.⁴

The four services, and what they will sell you

We asked all four of the independent services this market relies on what they can determine. Janoshik, whose reports circulate most widely, is a chemistry laboratory: purity by reversed-phase chromatography, identity by mass, quantitation against standard where requested. Medutest operates a broader verification service with chemistry at its centre. PeptideMeter is likewise a chemistry and verification operation. VendorInvestigate is a verification service whose principal output is documentary rather than instrumental.

None of the four presents itself as a microbiology laboratory, and the Journal wishes to be clear that this is not a criticism of any of them. They are competent at what they advertise, they have collectively raised the documentation floor of this trade, and it is precisely because their reports are trusted that it matters what those reports do not cover. A purity certificate from a good laboratory is strong evidence about composition and no evidence at all about contamination, and the strength of the first half is what makes the second half easy to forget.

Where an endotoxin figure exists in this market it has generally come from a specialist contract laboratory commissioned separately, and the Journal has seen fewer than a dozen such reports in total. Two of them accompanied vials we submitted ourselves.

What we submitted, and what came back

Between the second and fourth quarters the Journal purchased fourteen vials of lyophilised research peptide from nine suppliers, at catalogue prices, through ordinary channels and without identifying ourselves. Each was photographed sealed, logged, and stored at two to eight degrees on arrival. Twelve were submitted to a contract laboratory accredited to the general competence standard for testing laboratories for bacterial endotoxin determination by kinetic chromogenic assay, with method suitability established for each matrix. Two were submitted for a compendial sterility test by membrane filtration, which destroyed both.

We disclose the following limitations without being asked. Fourteen vials from nine suppliers is not a survey. Single determinations carry the uncertainty of single determinations. A negative sterility result on one vial says nothing about the batch it came from, for exactly the statistical reasons set out above. And a vial that has crossed a border in a padded envelope has a thermal and mechanical history we cannot reconstruct.

What the exercise establishes is narrower than a survey and, we think, worth publishing: that the tests exist, that they are commercially available to a private purchaser at a known price, that the numbers they return are interpretable against a calculable limit, and that nothing prevented any of the nine suppliers from commissioning them first.⁵

A note on method and sourcing

The compendial material in this article is drawn from the current general chapters of the United States Pharmacopeia and the European Pharmacopoeia, read in the original rather than in summary, and from the international standards on aseptic processing and on laboratory competence. Where a chapter has changed status recently — as the recombinant reagent chapters have — we say so, because a reader consulting an older edition will find a different framing.

Where the Journal reports a number it obtained itself, it states the laboratory’s accreditation status, the method family, whether method suitability was established, and the number of determinations. Where we report what a company told us, we distinguish an answer from a refusal and a refusal from a non-response, because those three things are routinely collapsed in coverage of this trade and they are not the same.

Corrections to this department are handled by the standards desk, which reads every letter and records the outcome in the log. Readers who believe a paragraph here overstates its evidence are asked to write to standards@compoundjournal.com; readers with documents to send, including certificates they would like read, should write to letters@compoundjournal.com. We do not publish correspondents’ names without permission and we do not identify the source of a certificate.

Readers should hold two facts together, uncomfortable as the combination is. The frameworks described here — endotoxin limits, sterility assurance, particulate ceilings — govern licensed parenteral medicines, and research-use material is under no obligation to meet them. That is a legal fact about obligation. It is not a reassurance, and nobody involved in the trade has ever suggested it was.