If hepatic THF levels are reduced, as in the case of most primates, the formate will accumulate producing metabolic acidosis . Clinical Toxicology Methanol is a toxic alcohol whose major symptoms of toxicity may be delayed, since toxicity is mediated by its metabolite-formic acid. Toxicity can be variable with methanol. The variation in latency time to the development of symptoms is due to the slow metabolism of methanol to formate. This latency phase can be further delayed by the co-ingestion of ethanol.
Methanol initially causes confusion and ataxia for several hours, similar to other alcohols.
After the ingestion a latency phase develops, during which methanol is being metabolized into formate. In this period the patient may present with malaise, headache, vomiting and abdominal pain. The clinical effects of methanol poisoning are highlighted by significant visual and neurological findings. This inhibition of cytochrome oxidase at the optic nerve is believed to result in edema of the optic disc and swelling of the myelin sheath which results in decreased visual acuity and pupillary responsiveness. Any patient with a history of alcohol ingestion who complains of decreased visual acuity needs an immediate fundus exam and visual fields testing by an ophthalmologist.