I expect GP mistook metformin-associated lactic acidosis in a patient with kidney disease as something metformin-caused. A separate but coincident IV misadministration could be an exacerbating factor. It would have been a rare case, but a plausible explanation for the misunderstanding.

Metformin is relatively kidney safe and not administered by IV. Thank you for clarifying that for anyone that may currently on or considering Metformin. It would be great if medical professionals were infallible communicators and had time to verify understanding, but they are human and we need more doctors and less time-pressure by profit extracting private equity.

Disclaimer: I am not a doctor.

I'll defer to your expertise. I wasn't there, and just sharing what aunt was "told".

I don't see any mention of IV in the OP comment.