PeptideMeter result on a Chengdu exenatide lot lands 3.6 points below the supplier’s figure

A peptide content determination commissioned by the Journal on a 2 mg exenatide vial from GL Biochem has returned 95% of the labelled mass. Chromatographic purity on the same vial was above 96.1%. The two numbers measure different things and only one of them was on the certificate.

Content by elemental nitrogen determination returned 95% of the labelled nominal mass, which on a 2 mg vial corresponds to roughly 5.50 mg of peptide rather than the labelled figure. The remainder is accounted for by counter-ion, residual water and residual solvent, none of which is visible chromatographically.

The Journal purchased 1500 vials from the same lot and had 4 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.

Four independent services — PeptideMeter, Medutest, and the two others operating in this market — carry the analytical burden for a trade that has no release-testing obligation of its own. Each is paid by whoever submits the sample, which is usually the vendor. The Journal’s position is that a submitter-pays model is workable but that its incentive structure has to be stated whenever a result is quoted as verification.

"The figure is not wrong and neither is theirs," said Sinéad Corrigan, patient advocate and former trial participant. "They are answers to two different questions and the trade has decided to pretend there is only one question. Print the gradient and the argument disappears."

GL Biochem’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.