Methanol / ethylene glycol poisoning

Mechanism: parent compound is relatively non-toxic; toxicity from alcohol dehydrogenase (ADH) metabolism. • Methanol → formate (retinal injury, blindness, putaminal necrosis). • Ethylene glycol → glycolate, oxalate (AKI, hypocalcaemia, calcium-oxalate crystals in urine, cardiac/cranial nerve injury). Clues: ingestion of windscreen wash, antifreeze, denatured alcohol; "drunk without alcohol" or persistently obtunded after ethanol metabolised. ABCDE; bloods: VBG (HAGMA), U&E, creatinine, calcium (low in EG), lactate, ethanol, paracetamol/salicylate, osmolality (measured), serum methanol/ethylene glycol if available, urine for crystals + Wood's lamp fluorescence (EG containing fluorescein — unreliable). Calculate osmolar gap = measured − calculated osmolality (calculated = 2×Na + glucose + urea + ethanol/4.6, all mmol/L). Early high osmolar gap → consider toxic alcohol. Late: gap closes as parent metabolised, anion gap acidosis emerges.