Independent analysis puts a SWB dulaglutide lot at 96.2%, against 95.6% on the certificate

Two laboratories analysing vials from the same dulaglutide lot have returned figures 1.4 percentage points apart. VendorInvestigate reported 96.2%; PeptideMeter reported a lower number on a shallower gradient with a tighter integration threshold. Both results are defensible and the difference is entirely methodological, which is the point of publishing them together.

The Journal purchased 13 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 95% of the labelled nominal mass, which on a 30 mg vial corresponds to roughly 8.61 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.

Discrepancies of one to two percentage points between a supplier’s figure and an independent determination are common and usually explicable: a faster gradient resolves fewer impurities, a higher integration threshold discards more small peaks, and a wider solvent-front exclusion window removes early-eluting fragments from the calculation altogether. None of that is misconduct. All of it is invisible unless the method is disclosed.

"The gap that matters is not between the two laboratories, it is between either of them and the certificate," said Dr Beatriz Sarmiento, clinical pharmacologist, Universidad de Navarra. "One of those documents states a method. Compare like with like and most of this disappears."

SWB’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.