Independent analysis puts a WXT exenatide lot at 97.4%, against 93.5% on the certificate

A peptide content determination commissioned by the Journal on a 10 mg exenatide vial from WXT has returned 90% of the labelled mass. Chromatographic purity on the same vial was above 97.4%. The two numbers measure different things and only one of them was on the certificate.

The Journal purchased 1700 vials from the same lot and had 18 of them analysed separately, in order to distinguish vial-to-vial variation from method variation. Vial-to-vial agreement was within 0.4 percentage points. Method-to-method disagreement was an order of magnitude larger.

Reported figures across the set were: highest 97.4%, lowest 93.5%, median close to the midpoint of the two. Every report in the set stated a detection wavelength, and 18 of them stated an integration threshold. The Journal has asked the laboratory to publish thresholds on all reports as a matter of routine.

Batch variance rather than vendor quality is the recurring finding of this programme. Across the 18 determinations the Journal has commissioned to date, within-vendor spread has been wider than between-vendor spread for two thirds of the companies tracked, which is an argument against rating any supplier on a single number.

"Content is the number that matters if you are doing arithmetic with a vial, and content is the number nobody sells," said Yusuf Kandemir, freight and customs broker, Istanbul. "Purity is what you can afford. Content is what you need."

WXT’s dossier has been updated with this determination and with the date of the request for comment. The dossier’s "what we could not verify" box records the questions still outstanding.