Metabolism of methanol and ethylene glycol and change in osmolal and anion gaps over time

Panel A is the metabolism of methanol and ethylene glycol. The enzyme for the first step is alcohol dehydrogenase, followed by aldehyde dehydrogenase producing the toxic acid metabolites.

Panel B shows the change in the osmolal (green lines) and anion (purple lines) gaps over time; the dashed lines show the delayed onset of these changes if alcohol dehydrogenase is inhibited (either by the coingestion of ethanol, or by antidotal therapy with either fomepizole or ethanol, but is not continued). Shortly after ingestion, an increased osmolal gap is prominent initially owing to the non-ionized alcohol itself and decreases as these alcohols are metabolized. Conversely, the anion gap is normal but increases as the ionized toxic acid metabolites accumulate.