• 4-Methylpyrazole;
  • Endogenous Ethanol;
  • Endogenous Methanol

Background: Endogenous methanol and ethanol levels are found in human blood. It is assumed that these compounds are derived mainly from microflora in the gastrointestinal tract and that the small amounts formed are consequently eliminated, mainly in the liver, by the alcohol dehydrogenase (ADH) pathway. The objective of the present study was to investigate the effect of 4-methylpyrazole (4-MP), a specific ADH inhibitor, on endogenous plasma methanol and ethanol levels in healthy women and men.

Methods: A double-blind placebo-controlled interventional study was carried out.

Results: A significant elevation in plasma endogenous ethanol and methanol levels was observed after intake of 4-MP (10–15 mg/kg p.o.). For methanol levels, a linear increase from 20 ± 14 μmol/l before intake to 39 ± 22 μmol/l at 420 min from intake of 4-MP (levels 20 ± 14 μmol/l and 14 ± 9 μmol/l during the corresponding placebo time points) was found. For ethanol, concentrations increased from levels below detection limit (i.e., < 5 μmol/l, determined by headspace gas chromatography) before intake to 30 ± 20 μmol/l at 195 min from intake of 4-MP. A small increase in ethanol levels, to 13 ± 8 μmol/l, but not in methanol levels, was observed after the intake of lingonberry juice containing no ethanol or methanol. No sex differences in the ethanol and methanol levels before or after the intake of 4-MP were found.

Conclusions: The present study provides conclusive evidence for a constant endogenous production as well as clearance of ethanol and methanol in humans. In addition, the study shows that the ethanol and methanol produced are, at least in part, eliminated by the ADH pathway.