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 95% of the labelled mass, the balance being the counter-ion and residual water that every lyophilised salt carries. Chromatographic purity on the same vial was above 97.4%. The two numbers measure different things, and this is one of the few certificates in the trade to print both.

The Journal purchased 20 vials from the same lot at retail and had four 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.

"Ask for the suitability summary before you argue about the percentage," said Lorcan Feeney, analytical services director at an independent laboratory. "If the tailing factor and the replicate precision are outside limits, you are arguing about arithmetic performed on an unfit separation."

WXT’s dossier has been updated with this determination and with the company’s response to it. The dossier’s ordering box records the lead times, the minimum quantities and what a buyer should ask for at the point of order.