Assessment

The lethal dose of methanol is about 1 g/kg (1.2 ml/kg). The minimum dose causing permanent visual defects is unknown.

Methanol itself is not very toxic, and there is usually a latent period of about 12 to 24 h between ingestion and the occurrence of symptoms. This is the time required for sufficient amounts of formic acid to accumulate. Since ethanol inhibits methanol metabolism, concomitant intake of ethanol may lengthen the latent period.

Clinical features are non-specific and include weakness, anorexia, headache, and nausea accompanied by increasing dyspnea (hyperventilation) as the metabolic acidosis develops. Visual symptoms (blurred vision) may appear first or together with the features described above. A few cases may present with acute pancreatitis or even methemoglobinemia.

There is usually little improvement of impaired visual acuity after the acute stage. The patient should always be evaluated by an ophthalmologist as the incident may have legal and insurance implications. The most severely poisoned patients may suffer from a Parkinson-like syndrome due to methanol-induced symmetrical lesions in the putamen.

The possibility of other methanol victims in addition to the treated patient should always be considered. Management

The treatment should follow the established principles of intensive care when needed. If the patient is seen within 1-2 h, gastric lavage should be performed. Activated charcoal is of no value.

The specific treatment of methanol poisoning includes administration of sodium bicarbonate to combat the metabolic acidosis, ethanol to inhibit metabolism of methanol to formate, and hemodialysis to remove methanol and formate.

Aggressive bicarbonate treatment must be given to correct the metabolic acidosis, to counteract the continuous production of organic acids, and to decrease the amount of undissociated formic acid and its access to the central nervous system. The aim should be full correction of the metabolic acidosis, i.e. as much as 400 to 600 mmol bicarbonate during the first few hours.

The therapeutic blood ethanol concentration of 22 mmol/l (1 g/l) may be attained by giving a bolus dose of 0.6 mg/kg of absolute ethanol, followed by 70 to 150 mg/kg/h intravenously (or orally) in dextrose-saline, with the highest maintenance dose for drinkers (1 g ethanol = 1.2 ml). Ethanol solutions above 20 per cent should be given via a central catheter. Monitoring of the blood ethanol level is important, particularly during hemodialysis which removes it. As a rule of thumb, the maintenance dose of ethanol should be doubled during hemodialysis.

Hemodialysis is indicated for any degree of visual impairment, provided that methanol or formate metabolic acidosis is still present, severe metabolic acidosis (base deficit above 15-20 mmol/l), blood methanol levels above 20 mmol/l (60 mg/dl), and if more than 40 ml has been ingested (adults). Hemodialysis should be performed for at least 8 h, as the blood half-life of methanol is 40 to 50 h (low pulmonary and renal excretion), with effective ethanol treatment.

Folinic acid (leucovorin) 50 to 70 mg (adult dose) should be given intravenously every 4 h for 24 h in order to enhance formate metabolism. Ethylene glycol

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