Independent analysis puts a FGP exenatide lot at 96.3%, against 92.6% on the certificate

A peptide content determination commissioned by the Journal on a 5 mg exenatide vial from FGP has returned 95% 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 96.3%. 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.

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.

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.

"Ask for the suitability summary before you argue about the percentage," said Dr Emiko Tanabe, mass spectrometrist. "If the tailing factor and the replicate precision are outside limits, you are arguing about arithmetic performed on an unfit separation."

FGP’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.