Formic acid in food: ingestion safety

Oral ingestion of formic acid causes corrosive GI injury combined with the risk of systemic formate toxicity — the same mechanism that makes methanol lethal (formate accumulation from methanol metabolism) applies to direct formic acid ingestion. GI corrosive injury: formic acid ingestion causes immediate burning pain and corrosive injury to oropharynx, esophagus, and stomach — similar in mechanism to acetic acid or hydrochloric acid, but with the additional systemic formate toxicity dimension. Systemic formate toxicity after ingestion: absorbed formate inhibits cytochrome c oxidase → cellular hypoxia → high anion gap metabolic acidosis; characteristic toxidrome includes: severe metabolic acidosis (pH <7.0 possible), visual disturbances (blurred vision, optic disc edema) → blindness, confusion, and circulatory collapse. Optic neuropathy: formate selectively injures the optic nerve (same mechanism as methanol poisoning's ocular toxicity) — visual loss from formate poisoning can be permanent; visual outcome depends on speed of treatment. Treatment: IV sodium bicarbonate for metabolic acidosis, folinic acid (leucovorin 1 mg/kg IV) to enhance folate-mediated formate oxidation, hemodialysis for severe toxicity (removes formate) — analogous to methanol poisoning treatment but without the need for ethanol or fomepizole as competitive inhibitor (no alcohol dehydrogenase step). Methanol poisoning connection: formic acid ingestion toxidrome is essentially the 'late phase' of methanol poisoning — presenting with the same optic neuropathy and metabolic acidosis caused by formate accumulation from methanol metabolism (methanol → formaldehyde → formate). Natural dietary formate: trace amounts in fruits and fermented foods are metabolized by folate-dependent enzymes with no systemic effect at dietary concentrations.