Medutest result on a Shenzhen tirzepatide lot lands 1.0 points below the supplier’s figure

A peptide content determination commissioned by the Journal on a 15 mg tirzepatide vial from WWB has returned 96% of the labelled mass. Chromatographic purity on the same vial was above 95.3%. The two numbers measure different things and only one of them was on the certificate.

Content by elemental nitrogen determination returned 96% of the labelled nominal mass, which on a 15 mg vial corresponds to roughly 9.87 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.

Content by elemental nitrogen determination returned 96% of the labelled nominal mass, which on a 15 mg vial corresponds to roughly 9.87 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 useful thing in that report is not the percentage, it is the system suitability data," said Alastair Renshaw, pharmaceutical supply-chain consultant. "It is the only part that tells you whether the percentage means anything."

WWB’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.