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


METHODS
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.


CONCLUSIONS
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.


CONCLUSIONS
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.
Hovda
Knut Erik
KE
Department of Acute Medicine, Ullevaal University Hospital, Oslo, Norway. kehovda@yahoo.com
Mundal
Haavard
H
Urdal
Petter
P
McMartin
Kenneth
K
Jacobsen
Dag
D
D000931:Antidotes / Q000627:therapeutic use; D017809:Fatal Outcome; D000077604:Fomepizole; D005561:Formates / Q000097:blood* / Q000652:urine; D006207:Half-Life; D006801:Humans; D008297:Male; D000432:Methanol / Q000097:blood / Q000506:poisoning* / Q000652:urine; D008875:Middle Aged; D011720:Pyrazoles / Q000627:therapeutic use; D006435:Renal Dialysis
D000931:Antidotes; D005561:Formates; D011720:Pyrazoles; C030544:formic acid; D000077604:Fomepizole; D000432:Methanol