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)
- increase elimination:
-> haemodialysis: effectively and rapidly removed including toxic metabolites
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