Methanol Toxicity

OVERVIEW

industrial solvent and synthetic precursor
highly variable lethal dose
in itself if is not very toxic, however metabolised to formaldehyde -> formic acid (neurotoxic – retina and optic nerves)

CLINICAL FEATURES

drunk: windshield fluid, antifreeze, paint, paint removers, gasoline, adhesives, glass cleaner, a solvent/cleaner.
symptoms develop 12-24 hours post ingestion
neurology: cerebral oedema, seizures, meningeal irritation, cerebral infarction, blurred vision -> blindness, scotomata, papilloedema, loss of light reflexes
respiratory failure
circulatory shock
GI symptoms

INVESTIGATIONS

raised osmolar gap
severe metabolic acidosis (raised anion gap)
methanol level (not useful acutely due to availability and turn around times)
normal ionized Ca2+

MANAGEMENT

decreased production of toxic metabolites:

-> ethanol (competitive inhibitor to alcohol dehydrogenase)
-> 4-methylapyrazole (same as ethanol but easier to titrate and no sedative effects)
-> sodium bicarbonate (undissociated formic acid more toxic than the dissociated product – give if pH < 7.3)
-> folinic acid: 50mg Q4hrly (decreases formate levels and decreases toxicity)