High doses of metformin, which can occur with very low GFR, may lead to increased lactate levels as a rare complication due to kidney excretion buildup.

“metformin is a weak mitochondrial toxin and as such it probably shouldn't be surprising that you'd have a higher level of lactate in medical school every student learns that one of the potential rare complications of metformin is lactic acidosis”

“if if you have very very high doses that can occur when you have very low GFR uh because metformin is excreted via the kidney if the metformin levels build up you can get lacast does that's a very very rare complication”