Clinical meaning
Methanol and ethylene glycol are toxic alcohols that are relatively harmless in their parent form but are metabolized by alcohol dehydrogenase (ADH) into highly toxic metabolites that cause severe end-organ damage and death if untreated. Methanol is oxidized by ADH to formaldehyde, then rapidly converted by aldehyde dehydrogenase to formic acid (formate). Formic acid inhibits cytochrome c oxidase (complex IV) in the mitochondrial electron transport chain, blocking aerobic metabolism and causing cellular energy failure. The retina and optic nerve are uniquely vulnerable due to their high metabolic demand and limited buffering capacity — formate accumulation produces retinal edema, optic disc hyperemia, and irreversible optic nerve demyelination, manifesting as blurred vision, central scotomata, and permanent blindness. Formic acid also causes severe high anion gap metabolic acidosis (HAGMA) with compensatory Kussmaul respirations. Ethylene glycol follows a parallel but distinct toxic pathway: ADH converts it to glycoaldehyde, then to glycolic acid (the primary cause of early HAGMA), and finally to oxalic acid. Oxalate chelates serum calcium to form insoluble calcium oxalate crystals that precipitate in the renal tubules, causing acute tubular necrosis (ATN),...