Extremely slow formate elimination in severe methanol poisoning: a fatal case report

Clin Toxicol (Phila). Jun-Aug 2007;45(5):516-21. doi: 10.1080/15563650701354150.

Abstract

Methanol poisoning is a potentially fatal medical emergency because of its metabolism to formic acid. The half-life of formate has been reported in the range of 2.5-12.5 hours, but the degree of inter-individual variation is not known. We studied methanol and formate kinetics in a case of late diagnosed methanol poisoning with persisting metabolic acidosis and circulatory failure.

Case report: A 63-year-old man was referred to our hospital with a tentative diagnosis of stroke. He was awake on admission, but he soon deteriorated in the emergency department and a metabolic acidosis was revealed. Methanol poisoning was then suspected approximately five hours after admission but in spite of intensive treatment he died after six days.

Results: The S-methanol half-lives during treatment with fomepizole before and during hemodialysis were 49.5 and 4.1 hours, respectively, while the similar half-lives of S-formate were 77.0 and 2.9 hours. S-fomepizole was measured and found to be within the therapeutic range during treatment.

Discussion: The patient was treated with the established dosing regimen for fomepizole and the measured S-fomepizole levels throughout the treatment were adequate; the S-methanol elimination also suggests that methanol metabolism was blocked. Hence, other explanations for this exceptionally long formate half-life include slow formate metabolism, due to small hepatic folate stores or to genetic deficiencies in formate-metabolizing enzymes, or slow formate excretion, due to renal tubular acidosis, to a non-oliguric renal failure, or to genetic deficiencies in the renal formate transporters.

Conclusion: This case report indicates that the half-life of S-formate may have greater inter-individual variation than earlier expected, being by far the longest half-life reported in the medical literature. These results support the use of hemodialysis in the treatment of such patients.

Publication types

  • Case Reports
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antidotes / therapeutic use
  • Fatal Outcome
  • Fomepizole
  • Formates / blood*
  • Formates / urine
  • Half-Life
  • Humans
  • Male
  • Methanol / blood
  • Methanol / poisoning*
  • Methanol / urine
  • Middle Aged
  • Pyrazoles / therapeutic use
  • Renal Dialysis

Substances

  • Antidotes
  • Formates
  • Pyrazoles
  • formic acid
  • Fomepizole
  • Methanol