VendorInvestigate result on a Qingdao retatrutide lot lands 3.6 points below the supplier’s figure

VendorInvestigate has published a purity determination of 99.1% on a 20 mg vial of retatrutide supplied by MKM, against a figure of 96.9% on the certificate that accompanied the vial. The sample was submitted by the Journal in April 2024 as part of a continuing programme of arm’s-length purchasing, and the vendor was told before the order was placed that any result would be published.

Content by elemental nitrogen determination returned 86% of the labelled nominal mass, which on a 20 mg vial corresponds to roughly 4.53 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 800 vials from the same lot and had 18 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.

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 useful thing in that report is not the percentage, it is the system suitability data," said Sinéad Corrigan, patient advocate and former trial participant. "It is the only part that tells you whether the percentage means anything."

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.