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 97% 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 98.9%. The two numbers measure different things, and this is one of the few certificates in the trade to print both.

The Journal purchased 12 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.

Content by elemental nitrogen determination returned 97% 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 quoted as a priced addition by most of the twenty companies in the Journal’s dossier programme rather than carried as a standard release test. Sterility and endotoxin are separate disciplines again, and are neither tested nor claimed.

Dr Emiko Tanabe, mass spectrometrist, thought the split-sample design was the useful part. "A single result on a single vial is an anecdote with a decimal point. Pairs from one lot to two laboratories is the cheapest experiment that answers a real question."

MKM’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.