Independent analysis puts a MKM cagrilintide lot at 98.9%, against 94.9% on the certificate

A peptide content determination commissioned by the Journal on a 5 mg cagrilintide vial from MKM has returned 94% of the labelled mass. Chromatographic purity on the same vial was above 98.9%. The two numbers measure different things and only one of them was on the certificate.

The Journal purchased 4700 vials from the same lot and had 22 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.

Content by elemental nitrogen determination returned 94% of the labelled nominal mass, which on a 5 mg vial corresponds to roughly 14.37 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.

Purity became this trade’s single figure of merit because it is the cheapest measurement to obtain and the easiest to compare. Peptide content, which determines how much drug is actually in a vial, costs several times as much and is not offered as a standard release test by any of the twenty companies in the Journal’s dossier programme. Sterility and endotoxin are separate disciplines again, and are neither tested nor claimed.

"The figure is not wrong and neither is theirs," said Havel Novotný, independent laboratory quality manager. "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."

MKM’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.